x86/guest-walk: use unambiguous register names

This is in preparation of eliminating the mis-naming of 64-bit fields
with 32-bit register names (eflags instead of rflags etc). Use the
guaranteed 32-bit underscore prefixed names for now where appropriate.

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

--- a/xen/arch/x86/mm/guest_walk.c
+++ b/xen/arch/x86/mm/guest_walk.c
@@ -196,7 +196,7 @@ guest_walk_tables(struct vcpu *v, struct
              *   - Page fault in kernel mode
              */
             smap = hvm_smap_enabled(v) &&
-                   ((hvm_get_cpl(v) == 3) || !(regs->eflags & X86_EFLAGS_AC));
+                   ((hvm_get_cpl(v) == 3) || !(regs->_eflags & X86_EFLAGS_AC));
             break;
         case SMAP_CHECK_ENABLED:
             smap = hvm_smap_enabled(v);