drm/bridge: ps8640: Use constant sleep time for polling hpd

The default hpd_wait_us in panel_edp.c is 2 seconds. This makes the
sleep time in the polling of _ps8640_wait_hpd_asserted become 200ms.
Change it to a constant 20ms to speed up the function.
Signed-off-by: Pin-yen Lin <treapking@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230331030204.1179524-1-treapking@chromium.org

drivers/gpu/drm/bridge/parade-ps8640.c

@@ -184,7 +184,7 @@ static int _ps8640_wait_hpd_asserted(struct ps8640 *ps_bridge, unsigned long wai
 	 * actually connected to GPIO9).
 	 */
 	ret = regmap_read_poll_timeout(map, PAGE2_GPIO_H, status,
-				       status & PS_GPIO9, wait_us / 10, wait_us);
+				       status & PS_GPIO9, 20000, wait_us);
 
 	/*
 	 * The first time we see HPD go high after a reset we delay an extra