powerpc: Don't silently handle machine checks from userspace

If a machine check comes from userspace we send a SIGBUS to the task and
fail to printk anything.

If we are taking machine checks due to bad hardware we want to know about
it right away. Furthermore if we don't complain loudly then it will look
a lot like a bug in the userspace application, potentially causing a lot
of confusion.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/traps.c

@@ -626,11 +626,6 @@ void machine_check_exception(struct pt_regs *regs)
 	if (recover > 0)
 		return;
 
-	if (user_mode(regs)) {
-		_exception(SIGBUS, regs, BUS_ADRERR, regs->nip);
-		return;
-	}
-
 #if defined(CONFIG_8xx) && defined(CONFIG_PCI)
 	/* the qspan pci read routines can cause machine checks -- Cort
 	 *