msm: ipa: fix release of already freed memory in SSR

In case an SSR occurs, and before the completion of the rmnet_ipa
driver initialization another SSR occurs, we are trying to free
memory that was previously freed and not yet reinitialized.
This fix is unregistering the rmnet_ipa driver only if it was
fully initialized.

CRs-fixed: 713824
Change-Id: Iab3ef35aea36baabf6f93ccb4670a77cc0fa50e8
Signed-off-by: Sivan Reinstein <sivanr@codeaurora.org>