f2fs: fix to initialize min_mtime with ULLONG_MAX

Since sit_i.min_mtime's type is unsigned long long, so we should
initialize it with max value of the type ULLONG_MAX instead of
LLONG_MAX.
Signed-off-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -3838,7 +3838,7 @@ static void init_min_max_mtime(struct f2fs_sb_info *sbi)
 
 	down_write(&sit_i->sentry_lock);
 
-	sit_i->min_mtime = LLONG_MAX;
+	sit_i->min_mtime = ULLONG_MAX;
 
 	for (segno = 0; segno < MAIN_SEGS(sbi); segno += sbi->segs_per_sec) {
 		unsigned int i;