staging: bcm2835-camera: Replace BUG_ON with return error

The error conditions don't warrant taking the kernel down, so remove
BUG_ON.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>