virtio_mmio: fix devm cleanup

Recent rework of the virtio_mmio probe/remove paths balanced a
devm_ioremap() with an iounmap() rather than its devm variant. This ends
up corrupting the devm datastructures, and results in the following
boot-time splat on arm64 under QEMU 2.9.0:

[    3.450397] ------------[ cut here ]------------
[    3.453822] Trying to vfree() nonexistent vm area (00000000c05b4844)
[    3.460534] WARNING: CPU: 1 PID: 1 at mm/vmalloc.c:1525 __vunmap+0x1b8/0x220
[    3.475898] Kernel panic - not syncing: panic_on_warn set ...
[    3.475898]
[    3.493933] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.15.0-rc3 #1
[    3.513109] Hardware name: linux,dummy-virt (DT)
[    3.525382] Call trace:
[    3.531683]  dump_backtrace+0x0/0x368
[    3.543921]  show_stack+0x20/0x30
[    3.547767]  dump_stack+0x108/0x164
[    3.559584]  panic+0x25c/0x51c
[    3.569184]  __warn+0x29c/0x31c
[    3.576023]  report_bug+0x1d4/0x290
[    3.586069]  bug_handler.part.2+0x40/0x100
[    3.597820]  bug_handler+0x4c/0x88
[    3.608400]  brk_handler+0x11c/0x218
[    3.613430]  do_debug_exception+0xe8/0x318
[    3.627370]  el1_dbg+0x18/0x78
[    3.634037]  __vunmap+0x1b8/0x220
[    3.648747]  vunmap+0x6c/0xc0
[    3.653864]  __iounmap+0x44/0x58
[    3.659771]  devm_ioremap_release+0x34/0x68
[    3.672983]  release_nodes+0x404/0x880
[    3.683543]  devres_release_all+0x6c/0xe8
[    3.695692]  driver_probe_device+0x250/0x828
[    3.706187]  __driver_attach+0x190/0x210
[    3.717645]  bus_for_each_dev+0x14c/0x1f0
[    3.728633]  driver_attach+0x48/0x78
[    3.740249]  bus_add_driver+0x26c/0x5b8
[    3.752248]  driver_register+0x16c/0x398
[    3.757211]  __platform_driver_register+0xd8/0x128
[    3.770860]  virtio_mmio_init+0x1c/0x24
[    3.782671]  do_one_initcall+0xe0/0x398
[    3.791890]  kernel_init_freeable+0x594/0x660
[    3.798514]  kernel_init+0x18/0x190
[    3.810220]  ret_from_fork+0x10/0x18

To fix this, we can simply rip out the explicit cleanup that the devm
infrastructure will do for us when our probe function returns an error
code, or when our remove function returns.

We only need to ensure that we call put_device() if a call to
register_virtio_device() fails in the probe path.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Fixes: 7eb781b1 ("virtio_mmio: add cleanup for virtio_mmio_probe")
Fixes: 25f32223

 ("virtio_mmio: add cleanup for virtio_mmio_remove")
Cc: Cornelia Huck <cohuck@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: weiping zhang <zhangweiping@didichuxing.com>
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>