V4L/DVB (5576): Improve / fix support for PAL-60 in cx25840

This causes the cx25840 module to treat V4L2_STD_PAL_60 similar to
other 60Hz timings, and it fixes a wrongly-named variable (timings are
independant of color system).

Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>