isdn: hfcsusb: Fix mISDN driver crash caused by transfer buffer on the stack

Since linux 4.9 it is not possible to use buffers on the stack for DMA transfers.

During usb probe the driver crashes with "transfer buffer is on stack" message.

This fix k-allocates a buffer to be used on "read_reg_atomic", which is a macro
that calls "usb_control_msg" under the hood.

Kernel 4.19 backtrace:

usb_hcd_submit_urb+0x3e5/0x900
? sched_clock+0x9/0x10
? log_store+0x203/0x270
? get_random_u32+0x6f/0x90
? cache_alloc_refill+0x784/0x8a0
usb_submit_urb+0x3b4/0x550
usb_start_wait_urb+0x4e/0xd0
usb_control_msg+0xb8/0x120
hfcsusb_probe+0x6bc/0xb40 [hfcsusb]
usb_probe_interface+0xc2/0x260
really_probe+0x176/0x280
driver_probe_device+0x49/0x130
__driver_attach+0xa9/0xb0
? driver_probe_device+0x130/0x130
bus_for_each_dev+0x5a/0x90
driver_attach+0x14/0x20
? driver_probe_device+0x130/0x130
bus_add_driver+0x157/0x1e0
driver_register+0x51/0xe0
usb_register_driver+0x5d/0x120
? 0xf81ed000
hfcsusb_drv_init+0x17/0x1000 [hfcsusb]
do_one_initcall+0x44/0x190
? free_unref_page_commit+0x6a/0xd0
do_init_module+0x46/0x1c0
load_module+0x1dc1/0x2400
sys_init_module+0xed/0x120
do_fast_syscall_32+0x7a/0x200
entry_SYSENTER_32+0x6b/0xbe

Signed-off-by: Juliana Rodrigueiro <juliana.rodrigueiro@intra2net.com>
Signed-off-by: David S. Miller <davem@davemloft.net>