test_power: Fix a bug in setting module parameter values

When the kernel loads a module, module params are processed prior to
calling module_init. As a result, setting module param value should not
have side effects, at least as long as the module has not been
initialized.

Signed-off-by: Andrey Gelman <andreyg@compulab.co.il>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>