Hardcode length of hardcoded char array instead of sizeof(long)

sizeof(long) != 8 on 32-bit.

Author: matoro

genext2fs.c

@@ -2293,7 +2293,7 @@ add2fs_from_tarball(filesystem *fs, uint32 this_nod, FILE * fh, int squash_uids,
 			continue;
 		} else
 			nbnull = 0;
-		if (memcmp(tarhead->ustar, "ustar\00000", sizeof(long)) && strcmp(tarhead->ustar, "ustar  "))
+		if (memcmp(tarhead->ustar, "ustar\00000", 8) && strcmp(tarhead->ustar, "ustar  "))
 			error_msg_and_die("not a tarball");
 		signed_checksum = unsigned_checksum = 0;
 		checksum = OCTAL_READ(tarhead->checksum);