fft: free the plan on the invalid word length path

The plan was allocated before the word-length switch and leaked when the
default case rejected an unsupported length. Free it before returning.

Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>

Author: lrgirdwo

src/math/fft/fft_common.c

@@ -53,6 +53,7 @@ struct fft_plan *fft_plan_common_new(struct processing_module *mod, void *inb,
 		break;
 	default:
 		comp_cl_err(mod->dev, "Invalid word length.");
+		mod_free(mod, plan);
 		return NULL;
 	}