Revert "r600g: Don't negate result of ABS instruction"

This reverts commit b6d4021393.

This actually breaks gears here on my rv670.

src/gallium/drivers/r600/r600_shader.c

@@ -1014,8 +1014,6 @@ static int tgsi_op2_s(struct r600_shader_ctx *ctx, int swap)
 			break;
 		case TGSI_OPCODE_ABS:
 			alu.src[0].abs = 1;
-			/* negation is performed after absolute value is taken */
-			alu.src[0].neg = 0;
 			break;
 		default:
 			break;