i4l: fix random freezes with AVM B1 drivers

i4l: fix random freezes with AVM B1 drivers

patch 9713d9e650045f7f2afd81d58a068827be306993 in mainline.

This fix the same issue which was debbuged for the C4 controller for the B1
versions.

The capilib_ function modify or traverse a linked list without locking.

This patch extends the existing locking to the calls of these function to
prevent access to a list which is in the middle of a modification.

Signed-off-by: Karsten Keil <kkeil@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>