x86/nested HAP: don't BUG() on legitimate error

set_p2m_entry() can fail without there being a bug in the code - crash
the domain rather than the host in that case.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/mm/hap/nested_hap.c
+++ b/xen/arch/x86/mm/hap/nested_hap.c
@@ -133,7 +133,7 @@ nestedhap_fix_p2m(struct vcpu *v, struct
         gdprintk(XENLOG_ERR,
 		"failed to set entry for %#"PRIx64" -> %#"PRIx64"\n",
 		L2_gpa, L0_gpa);
-        BUG();
+        domain_crash(p2m->domain);
     }
 }