x86/efi: fix improper use of lvalue

# HG changeset patch
# User Jeremy Fitzhardinge <jeremy@xensource.com>
# Date 1199391030 28800
# Node ID 5d35c92fdf0e2c52edbb6fc4ccd06c7f65f25009
# Parent  22f6a5902285b58bfc1fbbd9e183498c9017bd78
x86/efi: fix improper use of lvalue

pgd_val is no longer valid as an lvalue, so don't try to assign to it.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>