selftests/ftrace: Fix bashisms

Fix a few bashisms in ftrace selftests.

Link: http://lkml.kernel.org/r/5fbf4613eef0766918fa04e3ff537cae271223ee.1494956770.git.naveen.n.rao@linux.vnet.ibm.com



Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>