input: sensors: fix the status checking issue of akm09911

It checks the wrong register to tell if the akm09911 sensor is overflow
or not. Change it to fix potential akm09911 magnetic field overflow issue.

Change-Id: I5742b79303daf8b5fdb1a77e0ddc910012b6b445
Signed-off-by: Oliver Wang <mengmeng@codeaurora.org>