msm: mdm: use msleep instead of mdelay

Calling mdelay() for 2 seconds can cause a watchdog
bark because it is a blocking call intended to be
used where msleep() cannot be used such as in atomic
context. There is no need to use it here because
mdm_subsys_shutdown() will not be called in atomic
context.

Change-Id: Iecc4732e5ad20bfdf07b996ac4e9003383d382a8
Signed-off-by: Joel King <joelking@codeaurora.org>