x86/mce: Check regs before accessing it

x86/mce: Check regs before accessing it

commit 1acd85feba81084fcef00b73fc1601e42b77c5d8 upstream.

Commit in Fixes accesses pt_regs before checking whether it is NULL or
not. Make sure the NULL pointer check happens first.

Fixes: 0a5b288e85bb ("x86/mce: Prevent severity computation from being instrumented")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20211217102029.GA29708@kili
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>