x86, build: Make sure mkpiggy fails on read error

Ensure build doesn't silently continue despite read failure,
addressing a warning due to the unchecked call.

Signed-off-by: Daniel J Blueman <daniel.blueman@gmail.com>
LKML-Reference: <AANLkTimxxTMU3=4ry-_zbY6v1xiDi+hW9y1RegTr8vLK@mail.gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/boot/compressed/mkpiggy.c

@@ -62,7 +62,12 @@ int main(int argc, char *argv[])
 	if (fseek(f, -4L, SEEK_END)) {
 		perror(argv[1]);
 	}
-	fread(&olen, sizeof olen, 1, f);
+
+	if (fread(&olen, sizeof(olen), 1, f) != 1) {
+		perror(argv[1]);
+		return 1;
+	}
+
 	ilen = ftell(f);
 	olen = getle32(&olen);
 	fclose(f);