wpa_supplicant(hidl): Return value for get driver commands

The return value for the |wpa_drv_driver_cmd| for getter commands
contains the length of the buffer filled up. Unlike the other methods in
supplicant, this should be checked for < 0 for errors.

Bug: 35844946
Test: Verified that the mac address is fetched correctly.
Change-Id: I4462442ffbb97ff02450b7bc871fb3780beb2c14
(cherry picked from commit 3431fd2b55ff8d6cc49e044a1032e55828168b9e)
1 file changed