libata.h: add stub for ata_sas_port_resume

Fix build error when CONFIG_PM is not enabled by adding a stub
function in <linux/libata.h>.

drivers/scsi/libsas/sas_ata.c: In function 'sas_resume_sata':
drivers/scsi/libsas/sas_ata.c:756:3: error: implicit declaration of function 'ata_sas_port_resume' [-Werror=implicit-function-declaration]
Signed-off-by: NRandy Dunlap <rdunlap@infradead.org>
Reported-by: NJim Davis <jim.epost@gmail.com>
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>

include/linux/libata.h

@@ -1148,6 +1148,9 @@ static inline void ata_sas_port_suspend(struct ata_port *ap)
 static inline void ata_sas_port_async_resume(struct ata_port *ap)
 {
 }
+static inline void ata_sas_port_resume(struct ata_port *ap)
+{
+}
 #endif
 extern int ata_ratelimit(void);
 extern void ata_msleep(struct ata_port *ap, unsigned int msecs);