samples: kprobes: add missing MODULE_DESCRIPTION() macros

make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in samples/kprobes/kprobe_example.o
WARNING: modpost: missing MODULE_DESCRIPTION() in samples/kprobes/kretprobe_example.o

Add the missing invocations of the MODULE_DESCRIPTION() macro.

Link: https://lore.kernel.org/all/20240601-md-samples-kprobes-v1-1-b6a772353893@quicinc.com/Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

samples/kprobes/kprobe_example.c

@@ -125,4 +125,5 @@ static void __exit kprobe_exit(void)
 
 module_init(kprobe_init)
 module_exit(kprobe_exit)
+MODULE_DESCRIPTION("sample kernel module showing the use of kprobes");
 MODULE_LICENSE("GPL");

samples/kprobes/kretprobe_example.c

@@ -104,4 +104,5 @@ static void __exit kretprobe_exit(void)
 
 module_init(kretprobe_init)
 module_exit(kretprobe_exit)
+MODULE_DESCRIPTION("sample kernel module showing the use of return probes");
 MODULE_LICENSE("GPL");