wil6210: potential buffer overflow in wmi_evt_aoa_meas

The code in wmi_evt_aoa_meas can potentially overflow a data
buffer if the len parameter is smaller than
offsetof(struct wmi_aoa_meas_event, meas_data). Add protection
against this case.

Change-Id: I3f86f231e0c6b5ac54abbb9865cba0cbbd8d0448
Signed-off-by: Lior David <liord@codeaurora.org>