We dereference 'z' a few lines above this check.
If it was possible to hit this condition, it wouldve
triggered long ago, in the form of a crash.

Spotted with the source checker from Coverity.com.
Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>