selftests/ftrace: Check the first record for kprobe_args_type.tc

It is possible to get multiple records from trace during test and then more
than 4 arguments are assigned to ARGS.  This situation results in the failure
of kprobe_args_type.tc.  For example:
-----------------------------------------------------------
grep testprobe trace
   ftracetest-5902  [001] d... 111195.682227: testprobe: (_do_fork+0x0/0x460) arg1=334823024 arg2=334823024 arg3=0x13f4fe70 arg4=7
     pmlogger-5949  [000] d... 111195.709898: testprobe: (_do_fork+0x0/0x460) arg1=345308784 arg2=345308784 arg3=0x1494fe70 arg4=7
 grep testprobe trace
 sed -e 's/.* arg1=\(.*\) arg2=\(.*\) arg3=\(.*\) arg4=\(.*\)/\1 \2 \3 \4/'
ARGS='334823024 334823024 0x13f4fe70 7
345308784 345308784 0x1494fe70 7'
-----------------------------------------------------------

We don't care which process calls do_fork so just check the first record to
fix the issue.
Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_type.tc

@@ -38,7 +38,7 @@ for width in 64 32 16 8; do
   echo 0 > events/kprobes/testprobe/enable
 
   : "Confirm the arguments is recorded in given types correctly"
-  ARGS=`grep "testprobe" trace | sed -e 's/.* arg1=\(.*\) arg2=\(.*\) arg3=\(.*\) arg4=\(.*\)/\1 \2 \3 \4/'`
+  ARGS=`grep "testprobe" trace | head -n 1 | sed -e 's/.* arg1=\(.*\) arg2=\(.*\) arg3=\(.*\) arg4=\(.*\)/\1 \2 \3 \4/'`
   check_types $ARGS $width
 
   : "Clear event for next loop"