iio: imu: inv_mpu6050: Select I2C_MUX again

iio: imu: inv_mpu6050: Select I2C_MUX again

commit f7072198f217 ("iio: imu: Fix inv_mpu6050 dependencies")
undid the explicit selection of I2C_MUX previously
done by the driver, because I2C_MUX implicitly depended
on HAS_IOMEM.

However commit 93d710a65ef0 ("i2c: mux: fix up dependencies")
cleared up the situation properly and drivers that need
to select I2C_MUX can now do so again.

It makes a lot of sense for a driver to select the driver
infrastructure it needs so restore the natural order of
things.

Cc: Richard Weinberger <richard@nod.at>
Cc: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>