linux-user: Fix type for SIOCATMARK ioctl

The SIOCATMARK ioctl takes an argument which should be a
pointer to an integer where the kernel will write the result.
We were incorrectly declaring it as TYPE_NULL which would mean
it would always fail (with EFAULT) when it should succeed.
Correct the type.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>

linux-user/ioctls.h

@@ -120,7 +120,7 @@
                    MK_PTR(MK_STRUCT(STRUCT_fiemap)))
 #endif
 
-  IOCTL(SIOCATMARK, 0, TYPE_NULL)
+  IOCTL(SIOCATMARK, IOC_R, MK_PTR(TYPE_INT))
   IOCTL(SIOCGIFNAME, IOC_RW, MK_PTR(TYPE_INT))
   IOCTL(SIOCGIFFLAGS, IOC_W | IOC_R, MK_PTR(MK_STRUCT(STRUCT_short_ifreq)))
   IOCTL(SIOCSIFFLAGS, IOC_W, MK_PTR(MK_STRUCT(STRUCT_short_ifreq)))