at86rf230: fix commentation for symbol duration

This patch fix an copy&paste issue in the comment of setting symbol
duration. These comments are more correct according the at86rf212 datasheet
now.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/net/ieee802154/at86rf230.c

@@ -1043,10 +1043,10 @@ at86rf212_set_channel(struct at86rf230_local *lp, u8 page, u8 channel)
 		}
 	} else {
 		if (page == 0)
-			/* SUB:0 and BPSK:1 -> BPSK-20 */
+			/* SUB:0 and BPSK:1 -> OQPSK-100/200/400 */
 			lp->hw->phy->symbol_duration = 40;
 		else
-			/* SUB:1 and BPSK:1 -> BPSK-20 */
+			/* SUB:1 and BPSK:1 -> OQPSK-250/500/1000 */
 			lp->hw->phy->symbol_duration = 16;
 	}