soc: qcom: qmi_interface: Protect sk_user_data with RCU

sk_user_data can be protected with RCU instead of calling the callback
rwlock. RCU will ensure the pointer obtained in qmi_data_ready is
formed properly and cleanup can synchronize before continuing in handle
release.

Change-Id: I6a687bd7b311fe169a89cb959ae755730b81a9f1
Signed-off-by: Chris Lew <clew@codeaurora.org>