mips: missing syscall returns wrong errno

Return -TARGET_ENOSYS instead of -ENOSYS from linux-user/main.c
   * Caused strange 'Level 2 synchronization messages' instead of
correctly reporting the syscall was missing.
   * Made glibc simply fail instead of using older syscalls
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>
Signed-off-by: NWesley W. Terpstra <terpstra@debian.org>

linux-user/main.c

@@ -2080,7 +2080,7 @@ void cpu_loop(CPUMIPSState *env)
             syscall_num = env->active_tc.gpr[2] - 4000;
             env->active_tc.PC += 4;
             if (syscall_num >= sizeof(mips_syscall_args)) {
-                ret = -ENOSYS;
+                ret = -TARGET_ENOSYS;
             } else {
                 int nb_args;
                 abi_ulong sp_reg;