iio: adc: ltc2309: Fix endian type passed to be16_to_cpu()

Picked up by sparse.

Cc: Liam Beguin <[e-mail]>
Reviewed-by: Liam Beguin <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/adc/ltc2309.c

···
 				    unsigned long address, int *val)
 {
 	int ret;
-	u16 buf;
+	__be16 buf;
 	u8 din;
 
 	din = FIELD_PREP(LTC2309_DIN_CH_MASK, address & 0x0f) |