usb: gadget: f_cdev: Call function wakeup if func_wakeup_pending is set

Perform function wakeup from cser_resume if func_wakup_pending
flag is true. Set it again if the func_wakeup returns -EAGAIN.

Change-Id: If056327126e932911e3d832421b6171a50757e55
Signed-off-by: Prashanth K <quic_prashk@quicinc.com>