logalloc: Fix compilation error
logalloc: Fix compilation error

This patch moves a function using the region_impl type after the type
has been defined.

Signed-off-by: Duarte Nunes <a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>
Message-Id: <20170418124551.25369-1-a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>

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