atm: hide unused procfs functions

When CONFIG_PROC_FS is disabled, the function declarations for some
procfs functions are hidden, but the definitions are still build,
as shown by this compiler warning:

net/atm/resources.c:403:7: error: no previous prototype for 'atm_dev_seq_start' [-Werror=missing-prototypes]
net/atm/resources.c:409:6: error: no previous prototype for 'atm_dev_seq_stop' [-Werror=missing-prototypes]
net/atm/resources.c:414:7: error: no previous prototype for 'atm_dev_seq_next' [-Werror=missing-prototypes]

Add another #ifdef to leave these out of the build.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230516194625.549249-2-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/atm/resources.c

@@ -400,6 +400,7 @@ int atm_dev_ioctl(unsigned int cmd, void __user *buf, int __user *sioc_len,
 	return error;
 }
 
+#ifdef CONFIG_PROC_FS
 void *atm_dev_seq_start(struct seq_file *seq, loff_t *pos)
 {
 	mutex_lock(&atm_dev_mutex);
@@ -415,3 +416,4 @@ void *atm_dev_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
 	return seq_list_next(v, &atm_devs, pos);
 }
+#endif