MAINTAINERS: Fix file pattern for X86 MCE INFRASTRUCTURE

Code restructuring renamed arch/x86/kernel/cpu/mcheck/ to
be arch/x86/kernel/cpu/mce/

Update the MAINTAINERS file pattern to account for this change.

Fixes: 21afaf18 ("x86/mce: Streamline MCE subsystem's naming")
Reported-by: Joe Perches <joe@perches.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: https://lkml.kernel.org/r/20190325233416.GB8869@agluck-desk