MIPS: Use BUG_ON() where possible.

Based on original patch by Stoyan Gaydarov <stoyboyker@gmail.com> which
missed a few places.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index 137c14b..d934894 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -307,8 +307,7 @@
 				if (pmd_none(*pmd)) {
 					pte = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
 					set_pmd(pmd, __pmd((unsigned long)pte));
-					if (pte != pte_offset_kernel(pmd, 0))
-						BUG();
+					BUG_ON(pte != pte_offset_kernel(pmd, 0));
 				}
 				vaddr += PMD_SIZE;
 			}