iio: potentiometer: mcp4131: fix double application of wiper shift

commit 85e4614 upstream.

The MCP4131 wiper address is shifted twice when preparing the SPI
command in mcp4131_write_raw().

The address is already shifted when assigned to the local variable
"address", but is then shifted again when written to data->buf[0].
This results in an incorrect command being sent to the device and
breaks wiper writes to the second channel.

Remove the second shift and use the pre-shifted address directly
when composing the SPI transfer.

Fixes: 22d199a ("iio: potentiometer: add driver for Microchip MCP413X/414X/415X/416X/423X/424X/425X/426X")
Signed-off-by: Lukas Schmid <lukas.schmid@netcube.li>#
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: libschmudie-so

drivers/iio/potentiometer/mcp4131.c

@@ -222,7 +222,7 @@ static int mcp4131_write_raw(struct iio_dev *indio_dev,
 
 	mutex_lock(&data->lock);
 
-	data->buf[0] = address << MCP4131_WIPER_SHIFT;
+	data->buf[0] = address;
 	data->buf[0] |= MCP4131_WRITE | (val >> 8);
 	data->buf[1] = val & 0xFF; /* 8 bits here */