ia64: salinfo: placate defined-but-not-used warning

When CONFIG_PROC_FS is not set, proc_salinfo_show() is not used.  Mark the
function as __maybe_unused to quieten the warning message.

../arch/ia64/kernel/salinfo.c:584:12: warning: 'proc_salinfo_show' defined but not used [-Wunused-function]
  584 | static int proc_salinfo_show(struct seq_file *m, void *v)
      |            ^~~~~~~~~~~~~~~~~

Link: https://lkml.kernel.org/r/20230223034309.13375-1-rdunlap@infradead.org
Fixes: 3f3942ac ("proc: introduce proc_create_single{,_data}")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/ia64/kernel/salinfo.c

@@ -581,7 +581,7 @@ static int salinfo_cpu_pre_down(unsigned int cpu)
  * 'data' contains an integer that corresponds to the feature we're
  * testing
  */
-static int proc_salinfo_show(struct seq_file *m, void *v)
+static int __maybe_unused proc_salinfo_show(struct seq_file *m, void *v)
 {
 	unsigned long data = (unsigned long)v;
 	seq_puts(m, (sal_platform_features & data) ? "1\n" : "0\n");