MINOR: [C++] Add check for result of MakeExecNode (#13849)
MINOR: [C++] Add check for result of MakeExecNode (#13849)

ARROW-16894 added benchmarks for asof join node. This PR adds a call to `ASSERT_OK` to satisfy the warning that the `Result` returned by `MakeExecNode` was not checked.

Authored-by: Aldrin M <75c199c3a31b60f91567634037d820c919fad644@pm.me>
Signed-off-by: Weston Pace <0dd0706858a011bb30a3fd82b71cee4f9094c502@gmail.com>
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