lib/: Use [[gnu::alloc_size(...)]] on allocation functions

Suggested-by: Martin Uecker <uecker@tugraz.at>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

lib/alloc/malloc.h

@@ -19,6 +19,7 @@
 )
 
 
+ATTR_ALLOC_SIZE(1, 2)
 ATTR_MALLOC(free)
 inline void *mallocarray(size_t nmemb, size_t size);