staging: rtl8723au: Remove uses of MAC_FMT and MAC_ARG

Use the standard vsprintf kernel extension to format
mac addresses.

This reduces object code size a bit.

Miscellanea:

o Coalesce formats
o Realign arguments
o Remove the now unused MAC_FMT and MAC_ARG #defines

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>