mx6slevk: Fix the reset delay for the the LAN8720 PHY

Since commit 59370f3f ("net: phy: delay only if reset handler is
registered") Ethernet is no longer functional.

This commit does not have an issue in itself, but it revelead a problem
with the Ethernet initialization.

According to the LAN8720 datasheet tpurstd (time that reset line should
stay asserted) is 25ms.

So do as suggested in order to have Ethernet working again.
Signed-off-by: NFabio Estevam <fabio.estevam@nxp.com>

board/freescale/mx6slevk/mx6slevk.c

@@ -156,7 +156,7 @@ static void setup_iomux_fec(void)
 
 	/* Reset LAN8720 PHY */
 	gpio_direction_output(ETH_PHY_RESET , 0);
-	udelay(1000);
+	udelay(25000);
 	gpio_set_value(ETH_PHY_RESET, 1);
 }