This patch fixes an issue that sometimes this controller is not able
to complete the Control write status stage.

This driver should enable DCPCTR.CCPL and PID_BUF to complete the status
stage. However, if this driver detects the ctrl_stage interruption first
before the control write data is received, this driver will clear the
PID_BUF wrongly in the usbhsf_pio_try_pop(). To avoid this issue, this
patch doesn't clear the PID_BUF in the usbhsf_pio_try_pop().
(Since also the privious code doesn't disable the PID_BUF after a control
 transfer was finished, this patch doesn't have any side efforts.)

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>