msm: ipa: SW workaround for HW bug

Zero out a status scratch buffer used by IPA HW for generating
aggregation empty packet status. If this scratch buffer is not
cleared, we will see garbage in the aggr empty status packet
generated as a result of aggregation timer expiry or due to
aggregation force close.

Change-Id: I2c5fe334bf857211ce13ab85c98948f819742b2e
Signed-off-by: Ravi Gummadidala <rgummadi@codeaurora.org>