msm: ipa: fix race condition in ipa qmi service bringup

Due to a race condition between qmi server & qmi client in ipa
bringup after SSR, there's a need to make sure the curr_conn
pointer doesn't point to the old server connection during client
initialization in cases where the server disconnect callback
wasn't called before the client initialization.

CRs-fixed: 698486
Change-Id: I4f54c07c5c7ea2380f97ec7bff1eb98632777ec7
Signed-off-by: Sivan Reinstein <sivanr@codeaurora.org>