mtd: fix md5sum error checking

In mtd_verify(), the return value of md5sum() has been
interpreted as error if nonzero, while the function
returns number of processed bytes, which caused
mtd_verify() to always fail.

This patch fixes error checking to interpret only
negative values as errors.

Signed-off-by: Zefir Kurtisi <zefir.kurtisi@neratec.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44605 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/system/mtd/src/mtd.c

@@ -337,7 +337,7 @@ mtd_verify(const char *mtd, char *file)
 	if (quiet < 2)
 		fprintf(stderr, "Verifying %s against %s ...\n", mtd, file);
 
-	if (stat(file, &s) || md5sum(file, f_md5)) {
+	if (stat(file, &s) || md5sum(file, f_md5) < 0) {
 		fprintf(stderr, "Failed to hash %s\n", file);
 		return -1;
 	}