x86/boot: properly "ignore" early evaluated "no-real-mode"

The option parser takes off "no-" prefixes before matching, so they also
shouldn't be specified to match against.

Fixes: e44d986084 ("x86/setup: Ignore early boot parameters like no-real-mode")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/setup.c

@@ -692,7 +692,7 @@ static void __init noreturn reinit_bsp_stack(void)
  * has options that are only used during the very initial boot process,
  * so they can be ignored now.
  */
-ignore_param("no-real-mode");
+ignore_param("real-mode");
 ignore_param("edd");
 ignore_param("edid");