util: Fix GCC false-positive warning for CONTAINER_OF.

util: Fix GCC false-positive warning for CONTAINER_OF.

On sparc, GCC would issue the following warning for every use of
CONTAINER_OF:

    warning: cast increases required alignment of target type

This is a false positive: assuming that the data structure that it is
applied to was allocated properly, the use of CONTAINER_OF to reach it is
valid.  And if it was not allocated properly, then code that accesses it
other ways will have trouble too.