powerpc/mm/hugetlb: Don't panic when we don't find the default huge page size

The generic hugetlbfs code can handle not finding the default huge page
size correctly. With HPAGE_SHIFT = 0 we see in dmesg:

  hugetlbfs: disabling because there are no supported hugepage sizes

bash-4.2# echo 30 > /proc/sys/vm/nr_hugepages
bash: echo: write error: Operation not supported

Fixes: 03bb2d65900c ("powerpc: get hugetlbpage handling more generic")
Reported-by: Chris Smart <chris@distroguy.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/hugetlbpage.c

@@ -848,9 +848,6 @@ static int __init hugetlbpage_init(void)
 	else if (mmu_psize_defs[MMU_PAGE_2M].shift)
 		HPAGE_SHIFT = mmu_psize_defs[MMU_PAGE_2M].shift;
 #endif
-	else
-		panic("%s: Unable to set default huge page size\n", __func__);
-
 	return 0;
 }