net: macb: use bit access macro from header file

net: macb: use bit access macro from header file

macb.h provides macros for reading/setting bitfields,
in macb registers and descriptors. use that instead
of redefining them in the source file.

Signed-off-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Tested-by: Anup Patel <anup.patel@wdc.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>