Ib/core: Mark local uverbs_std_types functions to be static

Functions declared in uverbs_std_types.c are local to that file, but
they lack static declarations. This produces a lot of sparse warnings,
like the one below:

drivers/infiniband/core/uverbs_std_types.c:41:5: warning: symbol
				'uverbs_free_ah' was not declared.
				Should it be static?

So mark them as static.

CC: Matan Barak <matanb@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>