envsetup.sh: say -p for plain, not -ps.

toybox xxd treats -ps as -p -s with a missing argument to -s, rather
than as a bizarre synonym for -p.

Test: manual
Change-Id: Ia576861588a4ddeac9885bce8d718929b74f31b1

envsetup.sh

@@ -1095,7 +1095,7 @@ function is64bit()
 {
     local PID="$1"
     if [ "$PID" ] ; then
-        if [[ "$(adb shell cat /proc/$PID/exe | xxd -l 1 -s 4 -ps)" -eq "02" ]] ; then
+        if [[ "$(adb shell cat /proc/$PID/exe | xxd -l 1 -s 4 -p)" -eq "02" ]] ; then
             echo "64"
         else
             echo ""