fs: Make unload_nls() NULL pointer safe

Most call sites of unload_nls() do:
	if (nls)
		unload_nls(nls);

Check the pointer inside unload_nls() like we do in kfree() and
simplify the call sites.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Steve French <sfrench@us.ibm.com>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Cc: Petr Vandrovec <vandrove@vc.cvut.cz>
Cc: Anton Altaparmakov <aia21@cantab.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 8970d8c..04629d1 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -470,19 +470,11 @@
 
 	iput(sbi->fat_inode);
 
-	if (sbi->nls_disk) {
-		unload_nls(sbi->nls_disk);
-		sbi->nls_disk = NULL;
-		sbi->options.codepage = fat_default_codepage;
-	}
-	if (sbi->nls_io) {
-		unload_nls(sbi->nls_io);
-		sbi->nls_io = NULL;
-	}
-	if (sbi->options.iocharset != fat_default_iocharset) {
+	unload_nls(sbi->nls_disk);
+	unload_nls(sbi->nls_io);
+
+	if (sbi->options.iocharset != fat_default_iocharset)
 		kfree(sbi->options.iocharset);
-		sbi->options.iocharset = fat_default_iocharset;
-	}
 
 	sb->s_fs_info = NULL;
 	kfree(sbi);