vfs: link_path_walk: do '.' and '..' detection while hashing

vfs: link_path_walk: do '.' and '..' detection while hashing

Instead of loading the name again to detect '.' and '..', just use the
fact that we already had the masked last word available when as we
created the name hash.  Which is exactly what we'd then test for.

Dealing with big-endian word ordering needs a bit of care, particularly
since we have the byte-at-a-time loop as a fallback that doesn't do BE
word loads.  But not a big deal.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>