qemu: process: Minor language improvement in one of the SEV debug msgs

Be more consistent and use 'preparing' instead of 'prepare' here.
Signed-off-by: NLuyao Huang <lhuang@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>

src/qemu/qemu_process.c

@@ -5860,7 +5860,7 @@ qemuProcessPrepareSEVGuestInput(virDomainObjPtr vm)
     if (!sev)
         return 0;
 
-    VIR_DEBUG("Prepare SEV guest");
+    VIR_DEBUG("Preparing SEV guest");
 
     if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_SEV_GUEST)) {
         virReportError(VIR_ERR_INTERNAL_ERROR,