KVM: x86: set "mitigate_smt_rsb" storage-class-specifier to static

smatch reports
arch/x86/kvm/x86.c:199:20: warning: symbol
  'mitigate_smt_rsb' was not declared. Should it be static?

This variable is only used in one file so it should be static.

Signed-off-by: Tom Rix <trix@redhat.com>
Link: https://lore.kernel.org/r/20230404010141.1913667-1-trix@redhat.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: Tom Rix

arch/x86/kvm/x86.c

@@ -194,7 +194,7 @@ bool __read_mostly eager_page_split = true;
 module_param(eager_page_split, bool, 0644);
 
 /* Enable/disable SMT_RSB bug mitigation */
-bool __read_mostly mitigate_smt_rsb;
+static bool __read_mostly mitigate_smt_rsb;
 module_param(mitigate_smt_rsb, bool, 0444);
 
 /*