nvme-multipath: Fix memory leak with ana_log_buf

kmemleak reports a memory leak with the ana_log_buf allocated by
nvme_mpath_init():

unreferenced object 0xffff888120e94000 (size 8208):
  comm "nvme", pid 6884, jiffies 4295020435 (age 78786.312s)
    hex dump (first 32 bytes):
      00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00  ................
      01 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00  ................
    backtrace:
      [<00000000e2360188>] kmalloc_order+0x97/0xc0
      [<0000000079b18dd4>] kmalloc_order_trace+0x24/0x100
      [<00000000f50c0406>] __kmalloc+0x24c/0x2d0
      [<00000000f31a10b9>] nvme_mpath_init+0x23c/0x2b0
      [<000000005802589e>] nvme_init_identify+0x75f/0x1600
      [<0000000058ef911b>] nvme_loop_configure_admin_queue+0x26d/0x280
      [<00000000673774b9>] nvme_loop_create_ctrl+0x2a7/0x710
      [<00000000f1c7a233>] nvmf_dev_write+0xc66/0x10b9
      [<000000004199f8d0>] __vfs_write+0x50/0xa0
      [<0000000065466fef>] vfs_write+0xf3/0x280
      [<00000000b0db9a8b>] ksys_write+0xc6/0x160
      [<0000000082156b91>] __x64_sys_write+0x43/0x50
      [<00000000c34fbb6d>] do_syscall_64+0x77/0x2f0
      [<00000000bbc574c9>] entry_SYSCALL_64_after_hwframe+0x49/0xbe

nvme_mpath_init() is called by nvme_init_identify() which is called in
multiple places (nvme_reset_work(), nvme_passthru_end(), etc). This
means nvme_mpath_init() may be called multiple times before
nvme_mpath_uninit() (which is only called on nvme_free_ctrl()).

When nvme_mpath_init() is called multiple times, it overwrites the
ana_log_buf pointer with a new allocation, thus leaking the previous
allocation.

To fix this, free ana_log_buf before allocating a new one.

Fixes: 0d0b660f ("nvme: add ANA support")
Cc: <stable@vger.kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>