avr32:mmu.c: fix printf() length modifier

avr32 uses unsigned long addresses, fix the printf() length modifier for that
fact.

Before this patch following warning occours:

---8<---
mmu.c: In function 'mmu_init_r':
mmu.c:25: warning: format '%08x' expects type 'unsigned int', but argument 2 has type 'uintptr_t'
--->8---

Signed-off-by: Andreas Bießmann <biessmann@corscience.de>
cc: Mike Frysinger <vapier@gentoo.org>
cc: Thomas Chou <thomas@wytron.com.tw>
cc: Reinhard Meyer <u-boot@emk-elektronik.de>
Acked-by: Mike Frysinger <vapier@gentoo.org>