KVM: MTRR: exactly define the size of variable MTRRs

Only KVM_NR_VAR_MTRR variable MTRRs are available in KVM guest
Signed-off-by: NXiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -343,7 +343,7 @@ enum {
 };
 
 struct kvm_mtrr {
-	struct mtrr_var_range var_ranges[MTRR_MAX_VAR_RANGES];
+	struct mtrr_var_range var_ranges[KVM_NR_VAR_MTRR];
 	mtrr_type fixed_ranges[KVM_NR_FIXED_MTRR_REGION];
 	unsigned char enabled;
 	mtrr_type def_type;