Changed the rounding calculation for hblank and hsync to match it
to equations in cvt and gtf standards.

In cvt calculation, hsync needs to be rounded down.

In gtf calculations, hblank needs to be rounded to nearest multiple
of twice the cell granularity and hsync needs to be rounded to the
nearest multiple of cell granularity.

Cc: Martin Bugge <marbugge@cisco.com>
Signed-off-by: NPrashant Laddha <prladdha@cisco.com>
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>