[PPC] Fix modpost warning

Mark pte_alloc_one_kernel as __init_refok to fix the following warning:

WARNING: arch/ppc/mm/built-in.o(.text+0x1114): Section mismatch: reference to .init.text:early_get_page (between 'pte_alloc_one_kernel' and 'v_mapped_by_tlbcam')
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>

arch/ppc/mm/pgtable.c

@@ -92,7 +92,7 @@ void pgd_free(pgd_t *pgd)
 	free_pages((unsigned long)pgd, PGDIR_ORDER);
 }
 
-pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
+__init_refok pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
 {
 	pte_t *pte;
 	extern int mem_init_done;