usb: gadget: cdev: Fix spinlock recursion

Commit c99a841d ("usb: gadget: cdev: Add spinlock to synchronize
ports->cbits_updated")added spinlock to synchronize ports->cbits_updated
which is causing a spinlock recursion in usb_cser_notify_modem.

Fix this by unlocking the spinlock before it calls send_modem_ctrl_bits
which in turn tries to acquire the same spinlock.

Change-Id: I744ea93d7da60aaf27044400cf457cc81dab151d
Signed-off-by: Pratham Pratap <quic_ppratap@quicinc.com>