s390/sclp_vt220: fix unused function warning

When CONFIG_SCLP_VT220_TTY=y and CONFIG_SCLP_VT220_CONSOLE is not set:

../drivers/s390/char/sclp_vt220.c:771:13: warning: '__sclp_vt220_flush_buffer' defined but not used [-Wunused-function]
771 | static void __sclp_vt220_flush_buffer(void)

so move this function inside the #ifdef block where it is used.

Signed-off-by: Randy Dunlap <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Cc: Christian Borntraeger <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Heiko Carstens <[e-mail]>
Signed-off-by: Vasily Gorbik <[e-mail]>

drivers/s390/char/sclp_vt220.c

···
 }
 __initcall(sclp_vt220_tty_init);
 
+#ifdef CONFIG_SCLP_VT220_CONSOLE
+
 static void __sclp_vt220_flush_buffer(void)
 {
 	unsigned long flags;
···
 	}
 	spin_unlock_irqrestore(&sclp_vt220_lock, flags);
 }
-
-#ifdef CONFIG_SCLP_VT220_CONSOLE
 
 static void
 sclp_vt220_con_write(struct console *con, const char *buf, unsigned int count)