drm: xlnx: zynqmp_dpsub: Don't access connector in zynqmp_dp_set_format()

To prepare for the removal of the connector from the DP encoder, pass
the display info pointer to the zynqmp_dp_set_format() function instead
of accessing the connector internally. The display info is NULL when the
function is called at initialization time, as we have no display info at
that point. This doesn't change the existing behaviour, given that the
zynqmp_dp_set_format() was already handling this as a special case (the
display info isn't initialized at init time and is all zeroes).

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>