net: tc35815: Fix build error due to missed API change

Commit 7f854420 ("phy: Add API for {un}registering an mdio device to
a bus") introduces an API to access mii_bus structures, but missed to
update the tc35815 driver. This results in the following error message.

drivers/net/ethernet/toshiba/tc35815.c: In function 'tc_mii_probe':
drivers/net/ethernet/toshiba/tc35815.c:617:18: error:
	'struct mii_bus' has no member named 'phy_map'
drivers/net/ethernet/toshiba/tc35815.c:623:24: error:
	'struct mii_bus' has no member named 'phy_map'

Instead of looping over the list of phy addresses to find a phy chip,
use phy_find_first(). While the intent of the original code was to return
an error if more than one phy was specified, this code path was never
executed because the loop aborted after finding the first phy. The
original code is therefore semantically identical to phy_find_first(),
thus it is simpler and more straightforward to use phy_find_first()
directly.

Fixes: 7f854420

 ("phy: Add API for {un}registering an mdio device to a bus")
Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>