powerpc/mm: Remove redundant #if case

Remove the check of CONFIG_PPC_SUBPAGE_PROT when deciding if
is_hugepage_only_range() is extern or inline. The extern version is in
slice.c and is built if CONFIG_PPC_MM_SLICES=y.

There was no build break possible because CONFIG_PPC_SUBPAGE_PROT is
only selectable under conditions which also mean CONFIG_PPC_MM_SLICES
will be selected.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/hugetlb.h

@@ -71,7 +71,7 @@ pte_t *huge_pte_offset_and_shift(struct mm_struct *mm,
 
 void flush_dcache_icache_hugepage(struct page *page);
 
-#if defined(CONFIG_PPC_MM_SLICES) || defined(CONFIG_PPC_SUBPAGE_PROT)
+#if defined(CONFIG_PPC_MM_SLICES)
 int is_hugepage_only_range(struct mm_struct *mm, unsigned long addr,
 			   unsigned long len);
 #else