staging: pi433: fix naming when more than one radio is used

When using more than one hardware radio module pi433_probe fails as the
same name is used for all modules. Create unique name by adding minor
number to the device name.

Signed-off-by: Marcin Ciupak <marcin.s.ciupak@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>