mmc: build fix: mmc_pm_notify is only available with CONFIG_PM=y

This fixes a build breakage introduced by commit 4c2ef25fe0 ("mmc: fix
all hangs related to mmc/sd card insert/removal during suspend/resume")

Cc: David Brownell <david-b@pacbell.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: linux-mmc@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Acked-by: Maxim Levitsky <maximlevitsky@gmail.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/mmc/core/host.c

@@ -86,7 +86,9 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
 	init_waitqueue_head(&host->wq);
 	INIT_DELAYED_WORK(&host->detect, mmc_rescan);
 	INIT_DELAYED_WORK_DEFERRABLE(&host->disable, mmc_host_deeper_disable);
+#ifdef CONFIG_PM
 	host->pm_notify.notifier_call = mmc_pm_notify;
+#endif
 
 	/*
 	 * By default, hosts do not support SGIO or large requests.