x86: simplify do_iret() domain crashing

No need to issue distinct extra messages, domain_crash() prints file
name and line number, so in the event of a problem allows telling the
cases apart.

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

--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -293,9 +293,8 @@ unsigned long do_iret(void)
     if ( unlikely(copy_from_user(&iret_saved, (void *)regs->rsp,
                                  sizeof(iret_saved))) )
     {
-        gprintk(XENLOG_ERR,
-                "Fault while reading IRET context from guest stack\n");
-        goto exit_and_crash;
+        domain_crash(v->domain);
+        return 0;
     }
 
     /* Returning to user mode? */
@@ -303,9 +302,8 @@ unsigned long do_iret(void)
     {
         if ( unlikely(pagetable_is_null(v->arch.guest_table_user)) )
         {
-            gprintk(XENLOG_ERR,
-                    "Guest switching to user mode with no user page tables\n");
-            goto exit_and_crash;
+            domain_crash(v->domain);
+            return 0;
         }
         toggle_guest_mode(v);
     }
@@ -331,10 +329,6 @@ unsigned long do_iret(void)
 
     /* Saved %rax gets written back to regs->rax in entry.S. */
     return iret_saved.rax;
-
- exit_and_crash:
-    domain_crash(v->domain);
-    return 0;
 }
 
 static unsigned int write_stub_trampoline(