adb: keep mac build happy

Use FIONREAD instead of TIOCINQ

Change-Id: Ic9db0228a51c546a798c70f08f2e644a1a376120
diff --git a/fdevent.c b/fdevent.c
index b5dfb41..5c374a7 100644
--- a/fdevent.c
+++ b/fdevent.c
@@ -551,7 +551,7 @@
       subproc_fde->force_eof = 1;
 
       int rcount = 0;
-      ioctl(subproc_fd, TIOCINQ, &rcount);
+      ioctl(subproc_fd, FIONREAD, &rcount);
       D("subproc with fd=%d  has rcount=%d err=%d\n",
         subproc_fd, rcount, errno);