Rename UNUSED to UNUSED_ATTR in OSI due to symbol collision.

Change-Id: Ib26dbae713b3096adf2496f0ff0fcb607693b163

osi/include/osi.h

@@ -3,5 +3,5 @@
 #include <stdbool.h>
 #include <stdint.h>
 
-#define UNUSED __attribute__((unused))
+#define UNUSED_ATTR __attribute__((unused))
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))

osi/src/list.c

@@ -185,7 +185,7 @@ const list_node_t *list_begin(const list_t *list) {
 // this function returns the value of an invalid iterator for the given list.
 // When an iterator has the same value as what's returned by this function, you
 // may no longer call |list_next| with the iterator. |list| may not be NULL.
-const list_node_t *list_end(UNUSED const list_t *list) {
+const list_node_t *list_end(UNUSED_ATTR const list_t *list) {
   assert(list != NULL);
   return NULL;
 }