net: via/Kconfig: replace USE_OF with OF_???

USE_OF is used as intermediate Kconfig option by few
arch's (ARM, MIPS, Xtensa).
Replace instances of USE_OF outside of arch folders
with proper OF_???.

Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>