f2fs: mark is_extension_exist() inline

The caller set_file_temperature() is marked as inline as well.
It doesn't make much sense to leave is_extension_exist() un-inlined.
Signed-off-by: NPark Ju Hyung <qkrwngud825@gmail.com>
Reviewed-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/namei.c

@@ -143,7 +143,7 @@ static struct inode *f2fs_new_inode(struct inode *dir, umode_t mode)
 	return ERR_PTR(err);
 }
 
-static int is_extension_exist(const unsigned char *s, const char *sub)
+static inline int is_extension_exist(const unsigned char *s, const char *sub)
 {
 	size_t slen = strlen(s);
 	size_t sublen = strlen(sub);