MIPS: Fix KGDB build error

In file included from include/linux/ptrace.h:49,
                 from arch/mips/kernel/kgdb.c:25:
/home/yuasa/src/linux/test/mips/linux/arch/mips/include/asm/ptrace.h:123: error: expected declaration specifiers or '...' before '__s64'
/home/yuasa/src/linux/test/mips/linux/arch/mips/include/asm/ptrace.h:124: error: expected declaration specifiers or '...' before '__s64'
/home/yuasa/src/linux/test/mips/linux/arch/mips/include/asm/ptrace.h:126: error: expected declaration specifiers or '...' before '__u32'
/home/yuasa/src/linux/test/mips/linux/arch/mips/include/asm/ptrace.h:127: error: expected declaration specifiers or '...' before '__u32'
make[1]: *** [arch/mips/kernel/kgdb.o] Error 1

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>