Use dd command instead of test command to wait the Serial device

Author: hanyazou

tools/macosx/maple_upload

@@ -55,7 +55,7 @@ ${DFU_UTIL} -d ${usbID} -a ${altID} -D ${binfile} -R ${dfuse_addr} -R
 echo -n Waiting for ${dummy_port_fullpath} serial...
 
 COUNTER=0
-while [ ! -c ${dummy_port_fullpath} ] && ((COUNTER++ < 40)); do
+while ! dd if=${dummy_port_fullpath} of=/dev/null count=0 > /dev/null 2>&1 && ((COUNTER++ < 40)); do
     sleep 0.1
 done