isofs: fix potential memory leak in mount option parsing

When specifying string type mount option (e.g., iocharset)
several times in a mount, current option parsing may
cause memory leak. Hence, call kfree for previous one
in this case. Meanwhile, check memory allocation result
for it.
Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/isofs/inode.c

@@ -394,7 +394,10 @@ static int parse_options(char *options, struct iso9660_options *popt)
 			break;
 #ifdef CONFIG_JOLIET
 		case Opt_iocharset:
+			kfree(popt->iocharset);
 			popt->iocharset = match_strdup(&args[0]);
+			if (!popt->iocharset)
+				return 0;
 			break;
 #endif
 		case Opt_map_a: