ftrace: Maintain samples/ftrace

There's no entry in MAINTAINERS for samples/ftrace. Add one so that the
FTRACE maintainers are kept in the loop.

Link: https://lkml.kernel.org/r/20230103124912.2948963-2-mark.rutland@arm.comAcked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

MAINTAINERS

@@ -8570,6 +8570,7 @@ F:	kernel/trace/fgraph.c
 F:	arch/*/*/*/*ftrace*
 F:	arch/*/*/*ftrace*
 F:	include/*/ftrace.h
+F:	samples/ftrace
 
 FUNGIBLE ETHERNET DRIVERS
 M:	Dimitris Michailidis <dmichail@fungible.com>