video1394: remove BKL contention

video1394 does not need to take the BKL. The data structures shared between
file_operations and interrupts are already protected through context-specific
spinlocks.

The only other danger is video1394_release() being called during another
operation, however this cannot happen because release is only ever invoked
when the last thread has closed the fd.

Signed-off-by: Daniel Drake <ddrake@brontes3d.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>