input: sensors: fix the first akm09911 data is not available after enable

It takes about 7.2 ms for akm09911 to get valid data after single
measurement mode is set. Thus add some logic to wait until the data
is available.

CRs-fixed: 652168
Change-Id: I4f2d2117cd6f3e1dcfc2a27a692c211ac7990239
Signed-off-by: Oliver Wang <mengmeng@codeaurora.org>