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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/atm/resources.c

···
 	return error;
 }
 
+#ifdef CONFIG_PROC_FS
 void *atm_dev_seq_start(struct seq_file *seq, loff_t *pos)
 {
 	mutex_lock(&atm_dev_mutex);
···
 {
 	return seq_list_next(v, &atm_devs, pos);
 }
+#endif