x86: silence false log messages for plain "xpti" / "pv-l1tf"

While commit 2a3b34ec47 ("x86/spec-ctrl: Yet more fixes for xpti=
parsing")  claimed to have got rid of the 'parameter "xpti" has invalid
value "", rc=-22!' log message for "xpti" alone on the command line,
this wasn't the case (the option took effect nevertheless).

Fix this there as well as for plain "pv-l1tf".

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 2fb57e4bee
master date: 2018-09-28 17:12:14 +0200

xen/arch/x86/spec_ctrl.c

@@ -239,7 +239,7 @@ static __init int parse_pv_l1tf(char *s)
             else if ( (val = parse_boolean("domu", s, ss)) >= 0 )
                 opt_pv_l1tf = ((opt_pv_l1tf & ~OPT_PV_L1TF_DOMU) |
                                (val ? OPT_PV_L1TF_DOMU : 0));
-            else
+            else if ( *s )
                 rc = -EINVAL;
             break;
         }
@@ -690,7 +690,7 @@ static __init int parse_xpti(char *s)
             else if ( (val = parse_boolean("domu", s, ss)) >= 0 )
                 opt_xpti = (opt_xpti & ~OPT_XPTI_DOMU) |
                            (val ? OPT_XPTI_DOMU : 0);
-            else
+            else if ( *s )
                 rc = -EINVAL;
             break;
         }