ata: pata_ns87415: mark ns87560_tf_read static

The global function triggers a warning because of the missing prototype

drivers/ata/pata_ns87415.c:263:6: warning: no previous prototype for 'ns87560_tf_read' [-Wmissing-prototypes]
263 | void ns87560_tf_read(struct ata_port *ap, struct ata_taskfile *tf)

There are no other references to this, so just make it static.

Fixes: c4b5b7b6c4423 ("pata_ns87415: Initial cut at 87415/87560 IDE support")
Reviewed-by: Sergey Shtylyov <[e-mail]>
Reviewed-by: Serge Semin <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Damien Le Moal <[e-mail]>

drivers/ata/pata_ns87415.c

···
  *	LOCKING:
  *	Inherited from caller.
  */
-void ns87560_tf_read(struct ata_port *ap, struct ata_taskfile *tf)
+static void ns87560_tf_read(struct ata_port *ap, struct ata_taskfile *tf)
 {
 	struct ata_ioports *ioaddr = &ap->ioaddr;