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: I206ba01dfa989346ade769a0f68b372b21f84043
Signed-off-by: Gaurav Kashyap <quic_gaurkash@quicinc.com>
Signed-off-by: Pranav Lavhate <quic_plavhate@quicinc.com>