soc: qcom: glink_pkt: Remove incorrect mutex_unlock

When a channel is reset and a client is still reading, glink pkt
executes an error case. Remove the incorrect mutex_unlock in this case.

Change-Id: I2c28dadf327b09eaa55f9853e8bf1f55017c4e51
Signed-off-by: Chris Lew <clew@codeaurora.org>