Bluetooth: Fix slab-out-of-bounds read in hci_le_direct_adv_report_evt()

`num_reports` is not being properly checked. A malformed event packet with
a large `num_reports` number makes hci_le_direct_adv_report_evt() read out
of bounds. Fix it.

Cc: stable@vger.kernel.org
Fixes: 2f010b55 ("Bluetooth: Add support for handling LE Direct Advertising Report events")
Reported-and-tested-by:  <syzbot+24ebd650e20bd263ca01@syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?extid=24ebd650e20bd263ca01


Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>