util/nvmutil: use EXIT_FAILURE/SUCCESS for exits

this, in conjunction with the centralised exit scheme now
used by nvmutil, means that we have portable exit status.

notwithstanding the use of non-portable unix functions, and
especially the use of non-standard err.c (which GNU and BSD
libc implementations all have anyway, as does musl).

this code should now run on essentially any computer with
Linux or BSD on it.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/nvmutil/nvmutil.c

@@ -92,7 +92,7 @@ main(int argc, char *argv[])
 	writeGbe();
 
 	err_if((errno != 0) && (cmd != cmd_dump));
-	return errno ? 1 : 0;
+	return errno ? EXIT_FAILURE : EXIT_SUCCESS;
 }
 
 void
@@ -488,5 +488,5 @@ int
 set_err(int x)
 {
 	errno = errno ? errno : x;
-	return 1;
+	return EXIT_FAILURE;
 }