Fix build warnings:

1.
../drivers/ufs/host/ufs-mediatek.c:1375:5: error: no previous prototype for function 'ufs_mtk_system_suspend' [-Werror,-Wmissing-prototypes]
int ufs_mtk_system_suspend(struct device *dev)
    ^
../drivers/ufs/host/ufs-mediatek.c:1375:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
int ufs_mtk_system_suspend(struct device *dev)
^
static

2.
../drivers/ufs/host/ufs-mediatek.c:702:50: error: format specifies type 'unsigned long' but the argument has type 'int' [-Werror,-Wformat]
                snprintf(vcc_name, MAX_VCC_NAME, "vcc-ufs%lu", ver);
                                                         ~~~   ^~~
                                                         %d

Link: https://lore.kernel.org/r/20220623035052.18802-2-stanley.chu@mediatek.comReviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>