decode2: Minor cleanup

Remove unused variable is_reg in decode_input_reg_a.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

decode2.vhdl

@@ -53,10 +53,7 @@ architecture behaviour of decode2 is
 
 	function decode_input_reg_a (t : input_reg_a_t; insn_in : std_ulogic_vector(31 downto 0);
 				     reg_data : std_ulogic_vector(63 downto 0)) return decode_input_reg_t is
-		variable is_reg : std_ulogic;
 	begin
-		is_reg := '0' when insn_ra(insn_in) = "00000" else '1';
-
 		if t = RA or (t = RA_OR_ZERO and insn_ra(insn_in) /= "00000") then
 			--return (is_reg, insn_ra(insn_in), reg_data);
 			return ('1', insn_ra(insn_in), reg_data);