V4L/DVB (6793): Convert saa7134-empress to video_ioctl2

saa7134 were converted to video_ioctl2, but saa7134_empress weren't. This broke
saa7134-empress, since it were dependent of saa7134_common_ioctl.

With the conversion, the module had a size decrease of 436 bytes on x86_64:

   text    data     bss     dec     hex filename
   5196    4912       4   10112    2780 old/saa7134-empress.ko
   4760    4912       4    9676    25cc new/saa7134-empress.ko

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>