reflog: refactor cmd_reflog() to "if" branches

reflog: refactor cmd_reflog() to "if" branches

Refactor the "if" branches in cmd_reflog() to use "else if" instead,
and remove the whitespace between them.

As with 92f480909f7 (multi-pack-index: refactor "goto usage" pattern,
2021-08-23) this makes this code more consistent with how
builtin/{bundle,stash,commit-graph,multi-pack-index}.c look and
behave. Their top-level commands are all similar sub-command routing
functions.

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
Signed-off-by: Junio C Hamano <redacted>