msm: ipa: fix to not allow NAT DMA command without device initialization

Without NAT device initialization sending NAT DMA
commands leads to XPU violation. Added checks to
verify device initialized or not before sending DMA
command.

Change-Id: I7440abc14a81e1621573f0e2808a410d60b2458d
Acked-by: Ashok Vuyyuru <avuyyuru@qti.qualcomm.com>
Signed-off-by: Mohammed Javid <mjavid@codeaurora.org>