soc: qcom: smd: reset current_packet in OPENING state

In SSR case after re-opening the SMD channel the current_packet is
holding the stale data index of previous packet and reading from the
wrong index cause the unexpected results.

Reset the current packet index to zero in channel re-open case.

CRs-Fixed: 774297
Change-Id: Ie38fff2c56fdf43d5669c51a70e90000f9df6f14
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>