drm/panel: jh057n00900: Don't use magic constant

0xBF isn't in any ST7703 data sheet so mark it as unknown. This avoids
confusion on whether there is a missing command in that
dsi_generic_write_seq() call.
Signed-off-by: Guido Günther <agx@sigxcpu.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/7f50fa6de2ae029111f158f8ea7fd69a0903eb97.1561542477.git.agx@sigxcpu.org

drivers/gpu/drm/panel/panel-rocktech-jh057n00900.c

@@ -33,6 +33,7 @@
 #define ST7703_CMD_SETEXTC	 0xB9
 #define ST7703_CMD_SETMIPI	 0xBA
 #define ST7703_CMD_SETVDC	 0xBC
+#define ST7703_CMD_UNKNOWN0	 0xBF
 #define ST7703_CMD_SETSCR	 0xC0
 #define ST7703_CMD_SETPOWER	 0xC1
 #define ST7703_CMD_SETPANEL	 0xCC
@@ -94,7 +95,7 @@ static int jh057n_init_sequence(struct jh057n *ctx)
 	msleep(20);
 
 	dsi_generic_write_seq(dsi, ST7703_CMD_SETVCOM, 0x3F, 0x3F);
-	dsi_generic_write_seq(dsi, 0xBF, 0x02, 0x11, 0x00);
+	dsi_generic_write_seq(dsi, ST7703_CMD_UNKNOWN0, 0x02, 0x11, 0x00);
 	dsi_generic_write_seq(dsi, ST7703_CMD_SETGIP1,
 			      0x82, 0x10, 0x06, 0x05, 0x9E, 0x0A, 0xA5, 0x12,
 			      0x31, 0x23, 0x37, 0x83, 0x04, 0xBC, 0x27, 0x38,