4.9.80 compile failure with X86_VSYSCALL_EMULATION=n due to 9a0be5af

[Lennart Sorensen]

Commit 9a0be5af added a reference to vsyscall_pgprot in
arch/x86/mm/kaiser.c but that is undefined if X86_VSYSCALL_EMULATION=n
which on an embedded system where you know how all your software is
compiled is quite likely.

Of course the condition is always false with that config so the code
will never be run, but the compiler is unhappy.

-- 
Len Sorensen