efi_loader: correct HandleProtocol()

The UEFI specification requires that when a protocol is opened via
HandleProtocol() the agent handle is the image handle of the EFI firmware
(see chapter on EFI_BOOT_SERVICES.OpenProtocol()).

Let efi_handle_protocol() pass efi_root as agent handle to
efi_open_protocol().

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
index f5b5828..481f9b9 100644
--- a/lib/efi_loader/efi_boottime.c
+++ b/lib/efi_loader/efi_boottime.c
@@ -3073,7 +3073,7 @@
 					       const efi_guid_t *protocol,
 					       void **protocol_interface)
 {
-	return efi_open_protocol(handle, protocol, protocol_interface, NULL,
+	return efi_open_protocol(handle, protocol, protocol_interface, efi_root,
 				 NULL, EFI_OPEN_PROTOCOL_BY_HANDLE_PROTOCOL);
 }