efi_loader: efi_set_variable use const void *

The SetVariable() runtime service does not change the data passed to it.
So mark the parameter as constant.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/lib/efi_loader/efi_variable.c b/lib/efi_loader/efi_variable.c
index 4e6a04e..c302dbd 100644
--- a/lib/efi_loader/efi_variable.c
+++ b/lib/efi_loader/efi_variable.c
@@ -254,7 +254,7 @@
 /* http://wiki.phoenix.com/wiki/index.php/EFI_RUNTIME_SERVICES#SetVariable.28.29 */
 efi_status_t EFIAPI efi_set_variable(u16 *variable_name,
 				     const efi_guid_t *vendor, u32 attributes,
-				     efi_uintn_t data_size, void *data)
+				     efi_uintn_t data_size, const void *data)
 {
 	char *native_name = NULL, *val = NULL, *s;
 	efi_status_t ret = EFI_SUCCESS;