rt2x00: remove KSEG1ADDR define from rt2x00soc.h

Remove the KSEG1ADDR define from rt2x00soc.h as it redefines and covers the
correct one from the arch/mips/include/asm/addrspace.h. Otherwise the driver
oopses on the target platform (Ralink rt3050 board).

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>