ANDROID: Bluetooth: hidp: buffer overflow in hidp_process_report

The buffer length is unsigned at all layers, but gets cast to int and
checked in hidp_process_report and can lead to a buffer overflow.
Switch len parameter to unsigned int to resolve issue.

Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Fixes: 678af93e46ac10318b54f2f0c9abbdfe75c4e078 ("HID: Bluetooth: hidp: make sure input buffers are big enough")
Bug: 65853588
Change-Id: I779ce783ae7c3bce8c5a66c0954ef31347e42cfc