ata: libahci: make ahci_pmp_retry_softreset() as static

sparse says:

drivers/ata/libahci.c:1390:5: warning:
 symbol 'ahci_pmp_retry_softreset' was not declared. Should it be static?
Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

drivers/ata/libahci.c

@@ -1386,7 +1386,7 @@ static int ahci_bad_pmp_check_ready(struct ata_link *link)
 	return ata_check_ready(status);
 }
 
-int ahci_pmp_retry_softreset(struct ata_link *link, unsigned int *class,
+static int ahci_pmp_retry_softreset(struct ata_link *link, unsigned int *class,
 				    unsigned long deadline)
 {
 	struct ata_port *ap = link->ap;