Don't mask X_add_number containing a register number

It's obviously wrong to mask SPRs to 8 bits.

	PR 21118
	* config/tc-ppc.c (md_assemble): Don't mask register number.

gas/ChangeLog

@@ -1,3 +1,8 @@
+2017-12-12  Alan Modra  <amodra@gmail.com>
+
+	PR 21118
+	* config/tc-ppc.c (md_assemble): Don't mask register number.
+
 2017-12-07  Max Filippov  <jcmvbkbc@gmail.com>
 
 	* config/tc-xtensa.c (xg_order_trampoline_chain): Replace

gas/config/tc-ppc.c

@@ -3040,7 +3040,7 @@ md_assemble (char *str)
 		   && ex.X_add_number != 0
 		   && (operand->flags & PPC_OPERAND_GPR_0) != 0))
 	    as_warn (_("invalid register expression"));
-	  insn = ppc_insert_operand (insn, operand, ex.X_add_number & 0xff,
+	  insn = ppc_insert_operand (insn, operand, ex.X_add_number,
 				     ppc_cpu, (char *) NULL, 0);
 	}
       else if (ex.X_op == O_constant)