x86/platform/uv: Remove unused variable in UV5 NMI handler

Remove an unused variable.

Signed-off-by: Mike Travis <mike.travis@hpe.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20201013154731.132565-1-mike.travis@hpe.com