fprobe: add missing MODULE_DESCRIPTION() macro

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

Add the missing invocation of the MODULE_DESCRIPTION() macro.

Link: https://lore.kernel.org/all/20240601-md-samples-fprobe-v1-1-5d256a956612@quicinc.com/



Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>