iio: accel: mxc6255: Fix chip-id check

The initial commit adding support for the mxc6225 assumed the
mxc6225 has a chip-id of 0xe5 based on testing on a single Allwinner
A23 tablet with a mxc6225. Testing on a bunch of other Allwinner
tablets have shown that the chip-id for the mxc6225 is not constant.

A datasheet for the MXC6255 which I've found online says that bits
7 and 6 of the chip-id register are undefined (for the mxc6255), testing
on 5 different tablets with a mxc6225 has found the following ids:
0x25, 0x45, 0x65, 0x85, 0xe5. So it seems that for the mxc6225 bits
7, 6 and 5 of the chip-id register are undefined.

This commit adjusts the chip-id check so that the mxc6255 driver
properly recognizes the mxc6225 in all these tablets.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>