ioreq: allow arch_vcpu_ioreq_completion() to signal an error

Return false from arch_vcpu_ioreq_completion() when completion is not handled.
According to coding-best-practices.pandoc an error should be propagated to
caller, if caller is expecting to handle it, which seems to the case for
callers of arch_vcpu_ioreq_completion().

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Sergiy Kibrik <Sergiy_Kibrik@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/hvm/ioreq.c

@@ -47,7 +47,7 @@ bool arch_vcpu_ioreq_completion(enum vio_completion completion)
 
     default:
         ASSERT_UNREACHABLE();
-        break;
+        return false;
     }
 
     return true;

xen/include/xen/ioreq.h

@@ -118,7 +118,7 @@ bool arch_vcpu_ioreq_completion(enum vio_completion completion);
 static inline bool arch_vcpu_ioreq_completion(enum vio_completion completion)
 {
     ASSERT_UNREACHABLE();
-    return true;
+    return false;
 }
 #endif