PHTW register is selected based on default bit rate from Table[1].
for the bit rates less than or equal to 250. Currently first
value of default bit rate which is greater than or equal to
the caculated mbps is selected. This selection can be further
improved by selecting the default bit rate which is nearest to
the calculated value.

[1] specs r19uh0105ej0200-r-car-3rd-generation.pdf [Table 25.12]

Fixes: 769afd21 ("media: rcar-csi2: add Renesas R-Car MIPI CSI-2 receiver driver")
Signed-off-by: NSuresh Udipi <sudipi@jp.adit-jv.com>
Signed-off-by: NMichael Rodin <mrodin@de.adit-jv.com>
Reviewed-by: NNiklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: NHans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: NMauro Carvalho Chehab <mchehab+huawei@kernel.org>