iio: accel: bmc150: Move struct bmc150_accel_data definition to bmc150-accel.h

Further patches to bmc150-accel-i2c.c need to store some extra info
(on top of the second_dev pointer) in the bmc150_accel_data struct,
rather then adding yet more accessor functions for this lets just
move the struct bmc150_accel_data definition to bmc150-accel.h.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210523170103.176958-6-hdegoede@redhat.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>