usb: gadget: f_fs: Fix fence cleanup in ffs_dmabuf_transfer() error paths

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_fs: Fix fence cleanup in ffs_dmabuf_transfer() error paths The error paths for endpoint-disabled (ESHUTDOWN) and request-allocation failure (ENOMEM) in ffs_dmabuf_transfer() jump to err_fence_put which calls dma_fence_put() on the fence. However, at that point the fence has only been kmalloc'd — dma_fence_init() has not been called yet, so the refcount and the fence ops are uninitialized. Calling dma_fence_put() on such an object leads to undefined behavior. Use kfree() instead, since the fence is just a plain allocation at this stage, and rename the label to err_fence_free to reflect the actual cleanup action.