Correct error msg for sub:lvalue{%h{k}} in sassign

This:

    sub foo : lvalue { %hash{'key'} }
    foo = 3;

was incorrectly giving ‘Can't modify key/value hash slice in list
assignment’.  There is no list assignment there.

pp.c

@@ -5158,7 +5158,8 @@ PP(pp_kvhslice)
        if (flags) {
            if (!(flags & OPpENTERSUB_INARGS))
                /* diag_listed_as: Can't modify %s in %s */
-	       Perl_croak(aTHX_ "Can't modify key/value hash slice in list assignment");
+	       Perl_croak(aTHX_ "Can't modify key/value hash slice in %s assignment",
+				 GIMME_V == G_ARRAY ? "list" : "scalar");
 	   lval = flags;
        }
     }

t/op/kvhslice.t

@@ -8,7 +8,7 @@ BEGIN {
 
 # use strict;
 
-plan tests => 39;
+plan tests => 40;
 
 # simple use cases
 {
@@ -134,9 +134,13 @@ plan tests => 39;
     # lvalue subs in assignment
     {
         local $@;
-        eval 'sub bar:lvalue{ %h{qw(a b)} }; bar() = "1"';
+        eval 'sub bar:lvalue{ %h{qw(a b)} }; (bar) = "1"';
         like $@, qr{^Can't modify key/value hash slice in list assignment},
             'not allowed as result of lvalue sub';
+        eval 'sub bbar:lvalue{ %h{qw(a b)} }; bbar() = "1"';
+        like $@,
+             qr{^Can't modify key/value hash slice in scalar assignment},
+            'not allowed as result of lvalue sub';
     }
 }