selftest: ftrace: Fix to pick text symbols for kprobes

Fix to pick text symbols for multiple kprobe testcase.
kallsyms shows text symbols with " t " or " T " but
current testcase picks all symbols including "t",
so it picks data symbols if it includes 't' (e.g. "str").

This fixes it to find symbol lines with " t " or " T "
(including spaces).

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Reported-by: Russell King <linux@armlinux.org.uk>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>