x86 setup: correct the base in the GDT_ENTRY() macro

The GDT_ENTRY() macro in pm.c would incorrectly cut the bottom 8 bits
off the base.  We didn't define any bases with the bottom 8 bits
nonzero, so it is a non-manifest bug, but it's still a bug.

Pointed out by John Smith <johnsmith9344@gmail.com>.
Cc: John Smith <johnsmith9344@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>