gadgetfs: Fix leak on error in aio_read()

The previous fix, 'gadgetfs: use-after-free in ->aio_read()',
missed one error path where the iovec needs to be freed.

This fix is not needed upstream as that error path was removed
by commit 7fe3976e0f3a ('gadget: switch ep_io_operations to
->read_iter/->write_iter').

Fixes: f01d35a15fa0 ('gadgetfs: use-after-free in ->aio_read()')
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --cc drivers/usb/gadget/inode.c
Simple merge