kgdb: Return true in kgdb_nmi_poll_knock()

Fix the following coccicheck warning:

include/linux/kgdb.h:301:54-55: WARNING: return of 0/1 in function
'kgdb_nmi_poll_knock' with return type bool
Signed-off-by: NJason Yan <yanaijie@huawei.com>
Link: https://lore.kernel.org/r/20200507110649.37426-1-yanaijie@huawei.comSigned-off-by: NDaniel Thompson <daniel.thompson@linaro.org>

include/linux/kgdb.h

@@ -298,7 +298,7 @@ extern bool kgdb_nmi_poll_knock(void);
 #else
 static inline int kgdb_register_nmi_console(void) { return 0; }
 static inline int kgdb_unregister_nmi_console(void) { return 0; }
-static inline bool kgdb_nmi_poll_knock(void) { return 1; }
+static inline bool kgdb_nmi_poll_knock(void) { return true; }
 #endif
 
 extern int kgdb_register_io_module(struct kgdb_io *local_kgdb_io_ops);