catpt: Switch to use list_entry_is_head() helper

Since we got list_entry_is_head() helper in the generic header,
we may switch catpt to use it. It removes the need in additional variable.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20201214172138.44267-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>