msm: ipa4: Decrement number of packet in queue only if count was not zero

Decrement number of packet in ODL queue only if the count was not zero,
otherwise it was leading packet count value to negative value.

Change-Id: I21f913396f7062d4e175c923cf4f523a567f06a9
Acked-by: Ashok Vuyyuru <avuyyuru@qti.qualcomm.com>
Signed-off-by: Mohammed Javid <mjavid@codeaurora.org>