msm: ipa3: Protect access to ipa3_qmi_ctx variable by lock

ipa3_qmi_ctx is a global variable that may be accessed by
different worker threads. Protect the access to it
using mutex lock so that the access will be always atomic.

Change-Id: Iaf0c95d66817833c8e8123b12e94a7a01ab8df2c
CRs-fixed: 2056414
Signed-off-by: Ghanim Fodi <gfodi@codeaurora.org>