staging: et131x: Remove USE_FBR0 define and #ifdefs

USE_FBR0 has always been defined, even in the original driver code.
Remove the define and #ifdef code to leave the code in the same state.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>