[PARISC] fix compile break in use of lib/strncopy_from_user.c

Linus broke us with

commit 36126f8
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat May 26 10:43:17 2012 -0700

    word-at-a-time: make the interfaces truly generic

By moving functions defined in strncopy_from_user.c into the asm-geneic
version word-at-a-time.h.  Spark and OpenRisc were fixed to use this, but
not parisc.  Fix by adding to generic-y in asm/Kbuild

Signed-off-by: James Bottomley <JBottomley@Parallels.com>

arch/parisc/include/asm/Kbuild

@@ -1,3 +1,4 @@
 include include/asm-generic/Kbuild.asm
 
 header-y += pdc.h
+generic-y += word-at-a-time.h