runners: misc-flasher: hotfix

The 'command' command line argument for this flasher is now being
overridden by common code, which attaches the west subcommand name to
this.

Let's just hotfix this by renaming the argument in misc-flasher.
We can revisit the boundary between run_common.py arguments and
runners package arguments after the release.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>