cnss2: Add small delay after cold boot calibration shutdown

WLAN driver load may be queued right after cold boot calibration so
it results immediately powerup after shutdown which may cause PCIe link
training failure. Hence add a small delay after cold boot calibration
shutdown to avoid such issues.

Change-Id: I3e9495c1dcfdd560a5a314b9bc6e3b2a7aec36ba
Signed-off-by: Yue Ma <yuem@codeaurora.org>