staging: Use pr_warn instead of pr_warning

As said in commit f2c2cbcc ("powerpc: Use pr_warn instead of
pr_warning"), removing pr_warning so all logging messages use a
consistent <prefix>_warn style. Let's do it.

Cc: Karsten Keil <isdn@linux-pingi.de>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/r/20190920062544.180997-22-wangkefeng.wang@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/isdn/gigaset/interface.c

@@ -518,7 +518,7 @@ void gigaset_if_init(struct cardstate *cs)
 	if (!IS_ERR(cs->tty_dev))
 		dev_set_drvdata(cs->tty_dev, cs);
 	else {
-		pr_warning("could not register device to the tty subsystem\n");
+		pr_warn("could not register device to the tty subsystem\n");
 		cs->tty_dev = NULL;
 	}
 	mutex_unlock(&cs->mutex);