util/hash_table: Use FREE() to be consistent with the CALLOC_STRUCT() call

util/hash_table: Use FREE() to be consistent with the CALLOC_STRUCT() call

CALLOC_STRUCT() calls the OS abstraction layer to do the allocation.
Call FREE() to free the corresponding objects so we keep things
consistent and have proper debug traces when memory-debugging
is enabled.

Fixes: 6649b840c340 ("mesa/util: add a hash table wrapper which support 64-bit keys")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Yonggang Luo <luoyonggang@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26423>
(cherry picked from commit 977cc3157dc0215c065bc3039f7fd5c8b359dc17)