qcedev: check num_fds during unmap

check the num_fds passed into unmap buf ioctl,
or else it can lead to an out of bounds access.

Test: Build compilation. qcedev tests.

Change-Id: Ia6c0df1d630f4ff1d93d782d68e2a17edfb4d229
Signed-off-by: Gaurav Kashyap <quic_gaurkash@quicinc.com>
Signed-off-by: Pranav Lavhate <quic_plavhate@quicinc.com>