x86/mm/pat: Do not pass 'rb_root' down the memtype tree helper functions

Get rid of the passing the rb_root down the helper calls; there
is only one: &memtype_rbroot.

No change in functionality.

[ mingo: Fixed the changelog which described a different version of the patch. ]

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lkml.kernel.org/r/20191121011601.20611-3-dave@stgolabs.net


Signed-off-by: Ingo Molnar <mingo@kernel.org>