selftests/ftrace: Fix check of return value in fgraph-retval.tc test

selftests/ftrace: Fix check of return value in fgraph-retval.tc test

The addition of recording both the function name and return address to the
function graph tracer updated the selftest to check for "=-5" from "= -5".
But this causes the test to fail on certain configs, as "= -5" is still a
value that can be returned if function addresses are not enabled (older kernels).

Check for both "=-5" and " -5" as a success value.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Donglin Peng <pengdonglin@xiaomi.com>
Link: https://lore.kernel.org/20241011132042.435f43cc@gandalf.local.home
Fixes: 21e92806d39c6 ("function_graph: Support recording and printing the function return address")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>