The calculations from pixel rate, width+hblank, and height+vblank
do not give the correct framerate - it's half the speed it should
be.

The datasheet lists the default for the TIMING_HTS registers (0x380c/d)
as being 0x2d8 (728) which is less than the width of the image, so
the units clearly can't be pixels.
If TIMING_HTS is considered to be units of 2-pixels, then the
resulting value of 0x5b0 (1456) makes all the calculations correct.

This driver is reporting an HBLANK value of 250, with an image width
of 1280, so TIMING_HTS is 1530 (0x5fa) pixels. However it was also
setting the register to 0x5fa, thereby not taking into account it
being units of 2-pixels.

Correct the register value to 0x2fd so that all the timing calculations
give the correct results.
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>