ext2simg: fix error check of io_channel_read_blk64()

Check the return value of io_channel_read_blk64() correctly, considering
that it returns an errcode_t, which can be positive.

Fixes: db6f320912cf ("AOSP: android: add the ext2simg tool")
Change-Id: Iafc6c0169bc8ac79198f285da0246ff3b841ded8
Signed-off-by: Eric Biggers <ebiggers@google.com>
diff --git a/contrib/android/ext2simg.c b/contrib/android/ext2simg.c
index 13a9d56..d1b5dc4 100644
--- a/contrib/android/ext2simg.c
+++ b/contrib/android/ext2simg.c
@@ -88,7 +88,7 @@
 	bi->next = buf_list;
 	buf_list = bi;
 	retval = io_channel_read_blk64(fs->io, chunk_start, num_blks, bi->buf);
-	if (retval < 0)
+	if (retval)
 		ext2fs_fatal(retval, "reading data from %s", params.in_file);
 	if (sparse_file_add_data(s, bi->buf, len, chunk_start) < 0)