fat: Cleanup nls_unload() usage

Other users doesn't check NULL explicitly. So, these doesn't also
check to remove inconsistency.
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

fs/fat/inode.c

@@ -1497,10 +1497,8 @@ int fat_fill_super(struct super_block *sb, void *data, int silent,
 		iput(fat_inode);
 	if (root_inode)
 		iput(root_inode);
-	if (sbi->nls_io)
-		unload_nls(sbi->nls_io);
-	if (sbi->nls_disk)
-		unload_nls(sbi->nls_disk);
+	unload_nls(sbi->nls_io);
+	unload_nls(sbi->nls_disk);
 	if (sbi->options.iocharset != fat_default_iocharset)
 		kfree(sbi->options.iocharset);
 	sb->s_fs_info = NULL;