[LIBFSIMAGE] Further 64bit compile fix

64bit libext2fs can have __u64 defined as unsigned long long,
while a uint64_t is unsigned long, and GCC complains.

Signed-off-by: Tim Deegan <Tim.Deegan@xensource.com>

tools/libfsimage/ext2fs-lib/ext2fs-lib.c

@@ -119,7 +119,7 @@ ssize_t
 ext2lib_pread(fsi_file_t *file, void *buf, size_t nbytes, uint64_t off)
 {
 	ext2_file_t *f = fsip_file_data(file);
-	uint64_t tmpoff;
+	__u64 tmpoff;
 	unsigned int n;
 	int err;