V4L/DVB (8686): mt9m111: style cleanup

Fix a typo in Kconfig, simplify error checking, further minor cleanup.

Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Guennadi Liakhovetski <g.iakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>