ahci: wait longer for link.

I have observed timeouts on a cubietruck.

The increase to 40ms is completely arbitrary and Works For Me(tm). I
couldn't find a good reference for how long you are supposed to wait,
although googling around it seems like tens of ms rather than single
digits is more common. I don't think there is any harm in waiting a bit
longer.
Signed-off-by: NIan Campbell <ijc@hellion.org.uk>

drivers/block/ahci.c

@@ -41,7 +41,7 @@ u16 *ataid[AHCI_MAX_PORTS];
 #define WAIT_MS_SPINUP	20000
 #define WAIT_MS_DATAIO	5000
 #define WAIT_MS_FLUSH	5000
-#define WAIT_MS_LINKUP	4
+#define WAIT_MS_LINKUP	40
 
 static inline u32 ahci_port_base(u32 base, u32 port)
 {