media: platform: rzg2l-cru: Use v4l2_get_link_freq()

The rzg2l_csi2_calc_mbps() function currently tries to calculate the
link frequency for a CSI2 bus using the V4L2_CID_PIXEL_RATE control
of the remote subdevice. Switch the function to v4l2_get_link_freq()
which correctly targets V4L2_CID_LINK_FREQ before falling back on
V4L2_CID_PIXEL_RATE if the former is unavailable.

Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Daniel Scally <dan.scally+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20250625-rzg2l-cru-v6-3-a9099ed26c14@ideasonboard.com


Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>