V4L/DVB (4992): Fix typo in saa7134-dvb.c

Fix a typo (use_frontent -> use_frontend) in saa7134-dvb.c.

Signed-off-by: Stephan Berberig <s.berberig@arcor.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>