uefi: If MediaPresentSupported is false, assume media is present.

It seems the driver which runs the USB network dongle claims that that field is
not supported.

Change-Id: Ib5be399ef681ffab736270c845dda75676e04770
diff --git a/src/drivers/net/uefi.c b/src/drivers/net/uefi.c
index dc68000..9de5db1 100644
--- a/src/drivers/net/uefi.c
+++ b/src/drivers/net/uefi.c
@@ -117,12 +117,13 @@
 		return 1;
 	}
 
-	if (!snp->Mode->MediaPresentSupported) {
+	if (snp->Mode->MediaPresentSupported) {
+		*ready = snp->Mode->MediaPresent;
+	} else {
 		printf("Device doesn't support the MediaPresent field.\n");
-		return 1;
+		*ready = 1;
 	}
 
-	*ready = snp->Mode->MediaPresent;
 	return 0;
 }