cmd: efidebug: fix a wrong handling of arguments

Coverity detected a dead code, but actually there is a bug in a check
against a number of arguments. So simply fix it.

Reported-by: Coverity (CID 300330)
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>