MIPS: Set trap_no field in thread_struct on exception.

This reverts commit 7281cd22973008a782860e48ed8d85d00204168c and adds
actual functionality to use the field.
diff --git a/arch/mips/mm/fault.c b/arch/mips/mm/fault.c
index 852a41c..4b88fa03 100644
--- a/arch/mips/mm/fault.c
+++ b/arch/mips/mm/fault.c
@@ -57,12 +57,10 @@
 
 #ifdef CONFIG_KPROBES
 	/*
-	 * This is to notify the fault handler of the kprobes.	The
-	 * exception code is redundant as it is also carried in REGS,
-	 * but we pass it anyhow.
+	 * This is to notify the fault handler of the kprobes.
 	 */
 	if (notify_die(DIE_PAGE_FAULT, "page fault", regs, -1,
-		       (regs->cp0_cause >> 2) & 0x1f, SIGSEGV) == NOTIFY_STOP)
+		       current->thread.trap_nr, SIGSEGV) == NOTIFY_STOP)
 		return;
 #endif
 
@@ -224,6 +222,7 @@
 			print_vma_addr(" ", regs->regs[31]);
 			pr_info("\n");
 		}
+		current->thread.trap_nr = (regs->cp0_cause >> 2) & 0x1f;
 		info.si_signo = SIGSEGV;
 		info.si_errno = 0;
 		/* info.si_code has been set above */
@@ -282,6 +281,7 @@
 		       field, (unsigned long) regs->cp0_epc,
 		       field, (unsigned long) regs->regs[31]);
 #endif
+	current->thread.trap_nr = (regs->cp0_cause >> 2) & 0x1f;
 	tsk->thread.cp0_badvaddr = address;
 	info.si_signo = SIGBUS;
 	info.si_errno = 0;