msm: ipa: Fix post init in workqueue context

ipa post init is accessed from user space
context from ops structure.

While user space program triggered post init
there could be a chance, where the
user space context may get killed at any time,
due to which the memory allocation in post init
gets failed and in turn which clean up the
IPA driver.

Because the memory allocation of the
sigkill pending process will fail.

Make changes in ops structure write func-pointer to
queue a work instead of directly invoking post init.

So that ipa post init will execute in workqueue context.

Change-Id: Ia11b3a868d960111422c357bcc9924ef7b220e67
Acked-by: Mohammed Javid <mjavid@qti.qualcomm.com>
Signed-off-by: Utkarsh Saxena <usaxena@codeaurora.org>