spa: utils: defs: fix SPA_FOR_EACH_ELEMENT usage example

To iterate over an array of `T`, the iterator must be `(const) T *`,
so that the types are compatible when `T[]` decays into `T *`.

In the example when `struct foo *[]` decays, it becomes `struct foo **`,
which is not compatible with the the type of iterator, `struct foo *`.

Fix that by changing the type of the array to `struct foo[]`.

spa/include/spa/utils/defs.h

@@ -110,7 +110,7 @@ struct spa_fraction {
 /**
  * Array iterator macro. Usage:
  * ```c
- * struct foo *array[16];
+ * struct foo array[16];
  * struct foo *f;
  * SPA_FOR_EACH_ELEMENT(array, f) {
  *	f->bar = baz;