v4l2-ioctl: add a missing break at v4l_fill_fmtdesc()

The changeset ba300204 added a logic at the core to fill
the format description, however, a break is missing on one of
the formats, as reported by smatch:
	drivers/media/v4l2-core/v4l2-ioctl.c:1211 v4l_fill_fmtdesc() warn: missing break? reassigning 'descr'

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>