efivarfs: Make efivarfs_fill_super() static

sparse is complaining that efivarfs_fill_super() doesn't have a
prototype. Make it static to avoid the warning.

Cc: Xie ChanglongX <changlongx.xie@intel.com>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: Jeremy Kerr <jeremy.kerr@canonical.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

drivers/firmware/efivars.c

@@ -1004,7 +1004,7 @@ static int efivarfs_unlink(struct inode *dir, struct dentry *dentry)
 	return -EINVAL;
 };
 
-int efivarfs_fill_super(struct super_block *sb, void *data, int silent)
+static int efivarfs_fill_super(struct super_block *sb, void *data, int silent)
 {
 	struct inode *inode = NULL;
 	struct dentry *root;