x86/mce: Use idtentry_nmi_enter/exit()

The recent fix for NMI vs. IRQ state tracking missed to apply the cure
to the MCE handler.

Fixes: ba1f2b2e ("x86/entry: Fix NMI vs IRQ state tracking")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/87mu17ism2.fsf@nanos.tec.linutronix.de