Bluetooth: Fix for checking proper user-supplied buffers

During patch download procedure, size validation and zero
allocation of buffers are done to ensure values passed are
in permissible range.

CRs-fixed: 2082452
Change-Id: I16a46f8c8860296919bf11021143ae36f2964363
Signed-off-by: Balvinder Singh <bpsingh@codeaurora.org>