usb: gadget: f_fs: Fix memory leak for ipc_log_context

Driver is not calling ipc_log_context_destroy in driver
cleanup which leaves the context allocated.

Change-Id: Ic1a74b530836d142c9f1db2143b5700e8b6c3321
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>