mailbox: mtk-cmdq: add missing MODULE_DESCRIPTION() macro

make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/mailbox/mtk-cmdq-mailbox.o

Add the missing invocation of the MODULE_DESCRIPTION() macro.
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

drivers/mailbox/mtk-cmdq-mailbox.c

@@ -817,4 +817,5 @@ static void __exit cmdq_drv_exit(void)
 subsys_initcall(cmdq_drv_init);
 module_exit(cmdq_drv_exit);
 
+MODULE_DESCRIPTION("Mediatek Command Queue(CMDQ) Mailbox driver");
 MODULE_LICENSE("GPL v2");