efi_loader: Blt() with incorrect BltOperation

If EFI_GRAPHICS_OUTPUT_PROTOCOL.Blt() is called with an invalid value of
BltOperation return EFI_INVALID_PARAMETER.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_loader/efi_gop.c b/lib/efi_loader/efi_gop.c
index e003823..9428c3b 100644
--- a/lib/efi_loader/efi_gop.c
+++ b/lib/efi_loader/efi_gop.c
@@ -367,7 +367,7 @@
 					 dy, width, height, delta, vid_bpp);
 		break;
 	default:
-		ret = EFI_UNSUPPORTED;
+		ret = EFI_INVALID_PARAMETER;
 	}
 
 	if (ret != EFI_SUCCESS)