efi: Correct call to write_acpi_tables()

This must be passed a ulong, not a u64. Fix it to avoid LTO warnings on
sandbox.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/efi_loader/efi_acpi.c b/lib/efi_loader/efi_acpi.c
index 83f025e..f2b55b4 100644
--- a/lib/efi_loader/efi_acpi.c
+++ b/lib/efi_loader/efi_acpi.c
@@ -34,7 +34,7 @@
 	 * a 4k-aligned address, so it is safe to assume that
 	 * write_acpi_tables() will write the table at that address.
 	 */
-	write_acpi_tables(acpi);
+	write_acpi_tables((ulong)acpi);
 
 	/* And expose them to our EFI payload */
 	return efi_install_configuration_table(&acpi_guid,