MIPS: RB532: Remove {get,set}_434_reg()

These kernel symbols are unused. Also, since dev3 init has been moved to
devices.c, set_434_reg() breaks compiling as it uses dev3.

Signed-off-by: Phil Sutter <n0-1@freewrt.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>