pm: Move settting timeout to after suspending devices

pm_suspend_devices() could return an error. Set timeout using
sys_clock_set_timeout() to after this error is handled so that
we have the accurate power state when calling the timeout function.
This is useful in cases where we wish to compensate the
system timer for certain power modes.

Signed-off-by: Mahesh Mahadevan <mahesh.mahadevan@nxp.com>