[rl78] fix constant in pattern

[DJ Delorie]

This was causing the final pattern to not match.  Committed.

        * config/rl78/rl78-expand.md (one_cmplqi2): Make constant signed.

Index: config/rl78/rl78-expand.md
===================================================================
--- config/rl78/rl78-expand.md  (revision 205980)
+++ config/rl78/rl78-expand.md  (working copy)
@@ -174,13 +174,13 @@
      DONE;"
 )
 
 (define_expand "one_cmplqi2"
   [(set (match_operand:QI         0 "nonimmediate_operand")
        (xor:QI (match_operand:QI 1 "general_operand")
-               (const_int 255)))
+               (const_int -1)))
    ]
   ""
   "if (rl78_force_nonfar_2 (operands, gen_one_cmplqi2))
      DONE;"
 )