util/broadcom: Check for successful file access

Change-Id: I5c77b3c5ea3fbc249a8c564a521c2c3c45e1c560
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Found-by: Coverity Scan #1323510
Reviewed-on: https://review.coreboot.org/17877
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

util/broadcom/secimage/io.c

@@ -73,6 +73,11 @@ int DataRead(char *filename, uint8_t *buf, int *length)
 		return -1;
 	}
 	len = FileSizeGet(file);
+	if (len < 0) {
+		printf("Unable to seek in file: %s\n", filename);
+		fclose(file);
+		return -1;
+	}
 	if (len < *length)
 		*length = len;
 	else