usb: ks_bridge: Fix memory leaks in the driver

This change addresses two memory leaks:-
1) misc device is not getting deregistered during device
disconnect. Hence call misc_deregister() in disconnect.

2) Driver returns without freeing previous instances of
the driver data structure if memory allocation fails. Hence
free up memory allocated for ks_bridge structure.

Change-Id: I90133a002aa9d38597de8d1b21d3aad621552d46
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>