efi_loader: add missing const qualifier

This commit fixes the following compilation warning
of boottime->install_configuration_table() function.

lib/efi_selftest/efi_selftest_tcg2.c:475:46:
warning: passing argument 1 of ‘boottime->install_configuration_table’
discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  ret = boottime->install_configuration_table(&smbios_guid, dmi);

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/include/efi_api.h b/include/efi_api.h
index c8f959b..0accad0 100644
--- a/include/efi_api.h
+++ b/include/efi_api.h
@@ -120,7 +120,7 @@
 			struct efi_device_path **device_path,
 			efi_handle_t *device);
 	efi_status_t (EFIAPI *install_configuration_table)(
-			efi_guid_t *guid, void *table);
+			const efi_guid_t *guid, void *table);
 
 	efi_status_t (EFIAPI *load_image)(bool boot_policiy,
 			efi_handle_t parent_image,