Fix a minor typo in the comment. Added some comment, too.

Change-Id: I34c3b098b80b729c091ce27e56626b100ae3e9b3
diff --git a/src/mpool.c b/src/mpool.c
index b313e85..df954e8 100644
--- a/src/mpool.c
+++ b/src/mpool.c
@@ -182,7 +182,7 @@
 }
 
 /**
- * Allocates and entry from the given memory pool, if one is available. The
+ * Allocates an entry from the given memory pool, if one is available. The
  * fallback will not be used even if there is one.
  */
 static void *mpool_alloc_no_fallback(struct mpool *p)
@@ -201,6 +201,7 @@
 		goto exit;
 	}
 
+	/* There was no free list available. Try a chunk instead. */
 	chunk = p->chunk_list;
 	if (chunk == NULL) {
 		/* The chunk list is also empty, we're out of entries. */