iio: imu: Fix dependencies for !HAS_IOMEM archs

Not every arch has io memory.
While the driver has correct dependencies the select statement
will bypass the HAS_IOMEM dependency.
So, unbreak the build by rendering it into a real dependency.
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/imu/inv_mpu6050/Kconfig

@@ -5,9 +5,9 @@
 config INV_MPU6050_IIO
 	tristate "Invensense MPU6050 devices"
 	depends on I2C && SYSFS
+	depends on I2C_MUX
 	select IIO_BUFFER
 	select IIO_TRIGGERED_BUFFER
-	select I2C_MUX
 	help
 	  This driver supports the Invensense MPU6050 devices.
 	  This driver can also support MPU6500 in MPU6050 compatibility mode