usb: gadget: f_fs: add missing spinlock and mutex unlock

usb: gadget: f_fs: add missing spinlock and mutex unlock

This patch adds missing spin_unlock and mutex_unlock calls in
error handling code.

Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[backport from upstream commit 48968f8d5f2234fb1768c55cf7d96d0b87446cd6]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Change-id: I48968f8d5f2234fb1768c55cf7d96d0b87446cd6