staging: pi433: fix validation for min bit rate supported by the device

rf69 datasheets establishes that the minimum supported bit rate is
1.2 kbps regardless of modulation.

this patch replaces the errouneous validation with the correct value

Acked-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
Link: https://lore.kernel.org/r/20220118230413.GA4859@mail.google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>