x86/mce: Deduplicate exception handling

[ Upstream commit e42404af

 ]

Prepare code for further simplification. No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210908132525.096452100@linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>