dsp: voice_mhi: reset vote count at modem restart

MHI devote is not required when modem restarts during
a voice call, which results in PCIe down notification.
Hence, vote count is reset to zero when modem restart
is received.

Change-Id: Ia2a7bb98f21d5130520489c8f2d20a04d41f03b4
Signed-off-by: Vikram Panduranga <vpandura@codeaurora.org>