samples: subsys: input: draw_touch_events: set pixel format at runtime

Problem: On STM32U5G9J-DK1 + st_lcd_dsi_mb1835, the sample could BUS
FAULT with SCREEN_WIDTH_TO_CROSS_DIM=25 and show only a horizontal
line with 20.

Root cause: The tile buffer BPP is derived from the devicetree pixel
format (e.g., RGB888 = 3 BPP), but the driver may be using a
different current pixel format.

Fix: Explicitly set the driver pixel format to the DT-selected format at
init.

Signed-off-by: Charles Dias <charlesdias.cd@outlook.com>

Author: CharlesDias

samples/subsys/input/draw_touch_events/src/main.c

@@ -126,6 +126,14 @@ int main(void)
 		LOG_ERR("Unsupported BPP=%d", BPP);
 		return 0;
 	}
+
+	/* Ensure driver pixel format matches our buffer layout from DT */
+	int rc = display_set_pixel_format(display_dev, PIXEL_FORMAT);
+	if (rc < 0) {
+		LOG_WRN("display_set_pixel_format(%d) failed: %d, continuing with driver default",
+			PIXEL_FORMAT, rc);
+	}
+
 	fill_cross_buffer();
 	display_blanking_off(display_dev);