usb: f_cdev: Fix failure in function resume in f_cdev

Currently there is a fault in implementation of function suspend
and resume in f_cdev. In case when function suspend is issued
by the host and then cleared, still cser_resume is not being
performed. This is due to incorrect handling of if else
condition in usb_cser_func_suspend. Fix this by adding
proper handling.

Change-Id: I4f0e4c6c02d4b30f2fe0b67bc39a4fac9dbf96f1
Signed-off-by: Rohith Kollalsi <quic_rkollals@quicinc.com>