exfat: fix overflow in sector and cluster conversion

According to the exFAT specification, there are at most 2^32-11
clusters in a volume. so using 'int' is not enough for cluster
index, the return value type of exfat_sector_to_cluster() should
be 'unsigned int'.
Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

fs/exfat/exfat_fs.h

@@ -400,7 +400,7 @@ static inline sector_t exfat_cluster_to_sector(struct exfat_sb_info *sbi,
 		sbi->data_start_sector;
 }
 
-static inline int exfat_sector_to_cluster(struct exfat_sb_info *sbi,
+static inline unsigned int exfat_sector_to_cluster(struct exfat_sb_info *sbi,
 		sector_t sec)
 {
 	return ((sec - sbi->data_start_sector) >> sbi->sect_per_clus_bits) +