test_bpf: Add missing MODULE_DESCRIPTION()

make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in lib/test_bpf.o

Add the missing invocation of the MODULE_DESCRIPTION() macro.
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240531-md-lib-test_bpf-v1-1-868e4bd2f9ed@quicinc.com

lib/test_bpf.c

@@ -15706,4 +15706,5 @@ static void __exit test_bpf_exit(void)
 module_init(test_bpf_init);
 module_exit(test_bpf_exit);
 
+MODULE_DESCRIPTION("Testsuite for BPF interpreter and BPF JIT compiler");
 MODULE_LICENSE("GPL");