rt2x00: fix order of entry flags modification

In rt2800usb_work_txdone we check flags in order:

- ENTRY_OWNER_DEVICE_DATA
- ENTRY_DATA_STATUS_PENDING
- ENTRY_DATA_IO_FAILED

Modify flags in separate order in rt2x00usb_interrupt_txdone, to avoid
processing entries in _txdone with wrong flags or skip processing
ready entries.

Reported-by: Justin Piszcz <jpiszcz@lucidpixels.com>
Cc: stable@kernel.org
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>