x86/hyperv: Fix smp_ops build failure on UP kernels

CI testing found this build failure:

  arch/x86/hyperv/hv_crash.c:631:9: error: ‘smp_ops’ undeclared (first use in this function)

And I bisected it back to the initial commit that enabled this feature:

  77c860d is the first bad commit
  commit 77c860d (HEAD)
  Author: Mukesh Rathor <mrathor@linux.microsoft.com>
  Date:   Mon Oct 6 15:42:08 2025 -0700

  x86/hyperv: Enable build of hypervisor crashdump collection files

Hyperv should probably be limited to SMP kernels, as nobody
appears to be testing it on UP kernels.

Until then, fix the smp_ops assumption. Build tested only.

Fixes: 77c860d ("x86/hyperv: Enable build of hypervisor crashdump collection files")
Cc: Mukesh Rathor <mrathor@linux.microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Author: ingomolnar

arch/x86/hyperv/hv_crash.c

@@ -628,7 +628,9 @@ void hv_root_crash_init(void)
 	if (rc)
 		goto err_out;
 
+#ifdef CONFIG_SMP
 	smp_ops.crash_stop_other_cpus = hv_crash_stop_other_cpus;
+#endif
 
 	crash_kexec_post_notifiers = true;
 	hv_crash_enabled = true;