V4L/DVB (3790): Use after free in drivers/media/video/em28xx/em28xx-video.c

In several places we use dev->devno right after we kfree() dev.  This fixes
coverity bug id #1065

Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>