peep.c: Use constant when known over runtime

I imagine most compilers would know to optimize the reference away when
the first conditional has ruled out all but one possibility, but I think
it is clearer anyway to use that single value.

Author: khwilliamson

peep.c

@@ -2211,12 +2211,12 @@ S_maybe_multideref(pTHX_ OP *start, OP *orig_o, UV orig_action, U8 hints)
                 return;
             /* similarly for customised exists and delete */
             if (  (o->op_type == OP_EXISTS)
-               && PL_check[o->op_type] != Perl_ck_exists
-               && PL_check[o->op_type] != PL_check[PERL_CK_EXISTS])
+               && PL_check[OP_EXISTS] != Perl_ck_exists
+               && PL_check[OP_EXISTS] != PL_check[PERL_CK_EXISTS])
                 return;
             if (  (o->op_type == OP_DELETE)
-               && PL_check[o->op_type] != Perl_ck_delete
-               && PL_check[o->op_type] != PL_check[PERL_CK_DELETE])
+               && PL_check[OP_DELETE] != Perl_ck_delete
+               && PL_check[OP_DELETE] != PL_check[PERL_CK_DELETE])
                 return;
 
             if (   o->op_type != OP_AELEM