trace: ipc_logging: reset completion instead of reinitializing

init_completion() is being used to reinitialize the read completion
which will cause problems if complete_all() is ever used.

Use INIT_COMPLETION instead of init_completion() to reinitialize
the completion.

Change-Id: I33a78559d9debb6c90a039bd9f22f391c6c15f27
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>