EDAC/ghes: Change ghes_hw from global to static

Smatch reports this issue
  ghes_edac.c:44:3: warning: symbol 'ghes_hw' was not declared. Should it be static?

ghes_hw is used only in ghes_edac.c so change its storage-class
specifier to static.

Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220421135319.1508754-1-trix@redhat.com