powerpc: Remove stale calc_vm_prot_bits() comment

This comment is wrong, we wouldn't use calc_vm_prot_bits() here
because we are being called by calc_vm_prot_bits() to modify its
behaviour.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200703011958.1166620-2-npiggin@gmail.com

arch/powerpc/include/asm/mman.h

@@ -13,10 +13,6 @@
 #include <linux/pkeys.h>
 #include <asm/cpu_has_feature.h>
 
-/*
- * This file is included by linux/mman.h, so we can't use cacl_vm_prot_bits()
- * here.  How important is the optimization?
- */
 static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
 		unsigned long pkey)
 {