There are a few error paths which don't unlock the usbvision->lock.

So I've added mutex_unlock() calls to fix those paths.
Signed-off-by: NDaniel Walker <dwalker@mvista.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NThierry MERLE <thierry.merle@free.fr>
Signed-off-by: NMauro Carvalho Chehab <mchehab@infradead.org>