MIPS: ip22-gio: Make ip22_gio_set_64bit() and ip22_gio_init() static

These functions are used in only one file.
Made them static to fix the following build error:

arch/mips/sgi-ip22/ip22-gio.c:249:6: error: no previous prototype for ‘ip22_gio_set_64bit’ [-Werror=missing-prototypes]
arch/mips/sgi-ip22/ip22-gio.c:398:12: error: no previous prototype for ‘ip22_gio_init’ [-Werror=missing-prototypes]

Reported-by: k2ci <kernel-bot@kylinos.cn>
Signed-off-by: Genjian Zhang <zhanggenjian@kylinos.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>