x86: pci-calgary_64.c: make a variable static

"debugging" is a horrible name for a global variable - thankfully it can
become static.

Also put it out of __read_mostly so that gcc no longer has to emit it
at all.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>