s390/ctcm: add __printf format attribute to ctcm_dbf_longtext

Allow the compiler to recognize and check format strings and parameters.

As reported with allmodconfig and W=1:

drivers/s390/net/ctcm_dbug.c: In function ‘ctcm_dbf_longtext’:
drivers/s390/net/ctcm_dbug.c:73:9: error: function ‘ctcm_dbf_longtext’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
73 | vsnprintf(dbf_txt_buf, sizeof(dbf_txt_buf), fmt, args);
| ^~~~~~~~~

Acked-by: Julian Wiedmann <[e-mail]>
Signed-off-by: Heiko Carstens <[e-mail]>
Signed-off-by: Karsten Graul <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/s390/net/ctcm_dbug.h

···
 
 int ctcm_register_dbf_views(void);
 void ctcm_unregister_dbf_views(void);
+__printf(3, 4)
 void ctcm_dbf_longtext(enum ctcm_dbf_names dbf_nix, int level, char *text, ...);
 
 static inline const char *strtail(const char *s, int n)