wigig_sensing: return error code after change_mode failure

change_mode command sometimes fail. In such a case, a proper error code
should be returned to the calling user space application. Otherwise, the
application tries to read data, which is not available.

Change-Id: I03778cace54fd98847a099bbeaf7884cfbaac586
Signed-off-by: Gidon Studinski <gidons@codeaurora.org>