ipc: replace bool checks with explicit non-zero

ipc: replace bool checks with explicit non-zero

The function check_input() was returning a bool as error code.
It is changed to return an int, semantically more correct.
While at it, make checks of validate_action_name() return
explicit as described in the coding guidelines.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>