sparc32: avoid build warning at mm/percpu.c:1647

Fix following warning:

mm/percpu.c: In function 'pcpu_embed_first_chunk':
mm/percpu.c:1647:3: warning: format '%lx' expects type 'long unsigned int', but argument 3 has type 'unsigned int'

Signed-off-by: Daniel Hellstrom <daniel@gaisler.com>
[sam: added warning message to changelog, use _AC()]
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>