Bluetooth: change min_t() cast in hci_reassembly()

"count" is type int so the cast to __u16 truncates the high bits away
and triggers a Smatch static checker warning.  It looks like a high
value of count could cause a forever loop, but I didn't follow it
through to see if count is capped somewhere.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>