iio:vcnl4000: Mark transfer buffer as __be16

Fixes the following warnings from sparse:
drivers/iio/light/vcnl4000.c:88:16: warning: cast to restricted __be16
drivers/iio/light/vcnl4000.c:88:16: warning: cast to restricted __be16
drivers/iio/light/vcnl4000.c:88:16: warning: cast to restricted __be16
drivers/iio/light/vcnl4000.c:88:16: warning: cast to restricted __be16

Signed-off-by: Lars-Peter Clausen <[e-mail]>
Cc: Peter Meerwald <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/light/vcnl4000.c

···
 				u8 rdy_mask, u8 data_reg, int *val)
 {
 	int tries = 20;
-	u16 buf;
+	__be16 buf;
 	int ret;
 
 	ret = i2c_smbus_write_byte_data(data->client, VCNL4000_COMMAND,