usb: misc: Add snapshot of diag_bridge driver

USB diag host driver will be used to connect diag interface
exposed by Qualcomm devices. This is a snapshot of diag_bridge
driver from kernel msm-3.10 'commit 680769b57a70
("wcnss: Fix buffer overflow in wcnss_prealloc_get")'. Fix
checkpatch failures and minor code improvements.

Change-Id: Ide503c5bf729a7e41de98b12c89e4edc12af61fe
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>