drm/i915/dsi: Use TRANS_DDI_FUNC_CTL's own port width macro

The format of the port width field in the DDI_BUF_CTL and the
TRANS_DDI_FUNC_CTL registers are different starting with MTL, where the
x3 lane mode for HDMI FRL has a different encoding in the two registers.
To account for this use the TRANS_DDI_FUNC_CTL's own port width macro.

Cc: <stable@vger.kernel.org> # v6.5+
Fixes: b66a8aba ("drm/i915/display/mtl: Fill port width in DDI_BUF_/TRANS_DDI_FUNC_/PORT_BUF_CTL for HDMI")
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250214142001.552916-2-imre.deak@intel.com