drm/bridge: cdns-dsi: Fix event mode

drm/bridge: cdns-dsi: Fix event mode

The timings calculation gets it wrong for DSI event mode, resulting in
too large hbp value. Fix the issue by taking into account the
pulse/event mode difference.

Tested-by: Parth Pancholi <parth.pancholi@toradex.com>
Reviewed-by: Jayesh Choudhary <j-choudhary@ti.com>
Tested-by: Jayesh Choudhary <j-choudhary@ti.com>
Reviewed-by: Devarsh Thakkar <devarsht@ti.com>
Link: https://lore.kernel.org/r/20250723-cdns-dsi-impro-v5-13-e61cc06074c2@ideasonboard.com
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>