efi: drop volatile qualifier from "save gd" variables

The global gd pointer is no longer volatile-qualified, so drop that
qualifier from these bookkeeping variables.

Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

lib/efi_loader/efi_boottime.c

@@ -58,7 +58,7 @@ static efi_handle_t current_image;
  * restriction so we need to manually swap its and our view of that register on
  * EFI callback entry/exit.
  */
-static volatile gd_t *efi_gd, *app_gd;
+static gd_t *efi_gd, *app_gd;
 #endif
 
 efi_status_t efi_uninstall_protocol