x86/mm/cpa: Make cpa_data::numpages invariant

x86/mm/cpa: Make cpa_data::numpages invariant

Make sure __change_page_attr_set_clr() doesn't modify cpa->numpages.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom.StDenis@amd.com
Cc: dave.hansen@intel.com
Link: http://lkml.kernel.org/r/20181203171043.493000228@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>