Remove the function uwb_dev_addr_bcast() that is not used anywhere.

This was partially found by using a static code analysis program called cppcheck.
Signed-off-by: NRickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>