sound: usb: Unmap secondary event ring before freeing

USB secondary event ring is being freed before it is being unmap.
Fix this by calling xhci_sec_event_ring_cleanup() after unmapping.
Also move secondary event ring cleanup and unmap related duplicate
code into one API.

Change-Id: I420f53d9e3ad6aa7b310dc354c7d35ce139afbe9
Signed-off-by: Mayank Rana <mrana@codeaurora.org>