tools: moveconfig: fix --dry-run option

Since commit 96464bad ("moveconfig: Always run savedefconfig on
the moved config"), --dry-run option is broken.

The --dry-run option prevents the .config from being modified,
but defconfig files might be updated by "make savedefconfig"
regardless of the --dry-run option.

Move the "if not self.options.dry_run" conditional to the correct
place.

Fixes 96464bad ("moveconfig: Always run savedefconfig on the moved config")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>