ARM: mmp: avoid unused functions

mach-mmp/devices.c:81:21: warning: 'u2o_get' defined but not used [-Wunused-function]
 static unsigned int u2o_get(void __iomem *base, unsigned int offset)
                     ^
mach-mmp/devices.c:86:13: warning: 'u2o_set' defined but not used [-Wunused-function]
 static void u2o_set(void __iomem *base, unsigned int offset,
             ^
mach-mmp/devices.c:97:13: warning: 'u2o_clear' defined but not used [-Wunused-function]
 static void u2o_clear(void __iomem *base, unsigned int offset,
             ^
mach-mmp/devices.c:108:13: warning: 'u2o_write' defined but not used [-Wunused-function]
 static void u2o_write(void __iomem *base, unsigned int offset,
             ^

Signed-off-by: Arnd Bergmann <arnd@arndb.de>