efi_loader: fix incorrect use of EFI_EXIT()

efi_get_variable_common() does not use EFI_ENTRY(). So we should not use
EFI_EXIT() either.

Fixes: 767f6eeb01d3 ("efi_loader: variable: support variable authentication")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_loader/efi_variable.c b/lib/efi_loader/efi_variable.c
index 6271dbc..c262cb5 100644
--- a/lib/efi_loader/efi_variable.c
+++ b/lib/efi_loader/efi_variable.c
@@ -606,7 +606,7 @@
 	u32 attr;
 
 	if (!variable_name || !vendor || !data_size)
-		return EFI_EXIT(EFI_INVALID_PARAMETER);
+		return EFI_INVALID_PARAMETER;
 
 	ret = efi_to_native(&native_name, variable_name, vendor);
 	if (ret)