x86/mm: Stop prefetching current->mm->mmap_lock on page faults

x86/mm: Stop prefetching current->mm->mmap_lock on page faults

The prefetchw() dates back decades and the fundamental notion of doing
something like this on a lock is shady.

Moreover, for a few years now in the fast path faults are handled with RCU
+ per-vma locking, hopefully not even looking at the lock to begin with.

As such just remove it.

I did not see a point benchmarking this. Given that it is not expected
to be looked at by default justifies not doing the prefetch.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250401143520.1113572-1-mjguzik@gmail.com