[media] technisat-usb2: fix typo in variable name

The variable txlen was used instead of rxlen in boundary check.
(copy-paste error)

Signed-off-by: Felipe Pena <[e-mail]>
Signed-off-by: Michael Krufky <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/usb/dvb-usb/technisat-usb2.c

···
 	if (rxlen > 62) {
 		err("i2c RX buffer can't exceed 62 bytes (dev 0x%02x)",
 				device_addr);
-		txlen = 62;
+		rxlen = 62;
 	}
 
 	b[0] = I2C_SPEED_100KHZ_BIT;