staging: iio: ad9832: Remove redundant check

'val' is unsigned and cannot be negative.

Signed-off-by: Sachin Kamat <[e-mail]>
Cc: Michael Hennerich <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/staging/iio/frequency/ad9832.c

···
 		ret = spi_sync(st->spi, &st->msg);
 		break;
 	case AD9832_PHASE_SYM:
-		if (val < 0 || val > 3) {
+		if (val > 3) {
 			ret = -EINVAL;
 			break;
 		}