efi: app: Use the same efi_free_pool() signature as loader

The app has a function of this name, but it does not return any value.
Return success (always) so that we can use the same signature.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/efi.h

@@ -662,6 +662,14 @@ void *efi_malloc(struct efi_priv *priv, int size, efi_status_t *retp);
  */
 void efi_free(struct efi_priv *priv, void *ptr);
 
+/**
+ * efi_free_pool() - free memory from pool
+ *
+ * @buffer:	start of memory to be freed
+ * Return:	status code
+ */
+efi_status_t efi_free_pool(void *buffer);
+
 /**
  * efi_puts() - Write out a string to the EFI console
  *