rt2x00usb: remove unnecessary rx flag checks

In contrast to the TX path, there is no need to separately read the transfer
status from the device after receiving RX data. Consequently, there is no
real STATUS_PENDING RX processing queue entry state.
Remove the unnecessary ENTRY_DATA_STATUS_PENDING flag checks from the RX path.
Also remove the misleading comment about reading RX status from device.

Suggested-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Soeren Moch <smoch@web.de>
Acked-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>