drm/i915/dsi: Fix off by one in BXT_MIPI_TRANS_VTOTAL

drm/i915/dsi: Fix off by one in BXT_MIPI_TRANS_VTOTAL

BXT_MIPI_TRANS_VTOTAL must be programmed with vtotal-1
instead of vtotal. Make it so.

Cc: stable@vger.kernel.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250314150136.22564-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit 7b3685c9b38c3097f465efec8b24dbed63258cf6)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>