platform/chrome: cros_ec_sensorhub: Allocate sensorhub resource before claiming sensors

Allocate callbacks array before enumerating the sensors: The probe routine
for these sensors (for instance cros_ec_sensors_probe) can be called
within the sensorhub probe routine (cros_ec_sensors_probe())

Fixes: 145d59ba

 ("platform/chrome: cros_ec_sensorhub: Add FIFO support")
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reported-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>