staging: dgnc: replace udelay with usleep_range

Fix checkpatch warning on dgnc_cls.c: CHECK usleep_range is preferred
over udelay. udelay(t) in function cls_uart_init is within non-atomic
context and can be safely replaced by usleep_range(t, t + delta) where
delta is t (as t is between 10 and 20 microseconds).

Signed-off-by: Aishwarya Pant <aishpant@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>