memstick: fix hangs on unexpected device removal in mspro_blk

mspro_block_remove() is called from detect thread that first calls the
mspro_block_stop(), which stops the request queue.  If we call
del_gendisk() with the queue stopped we get a deadlock.

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Cc: Alex Dubov <oakad@yahoo.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>