net: phy: check return code when requesting PHY driver module

When requesting the PHY driver module fails we'll bind the genphy
driver later. This isn't obvious to the user and may cause, depending
on the PHY, different types of issues. Therefore check the return code
of request_module(). Note that we only check for failures in loading
the module, not whether a module exists for the respective PHY ID.

v2:
- add comment explaining what is checked and what is not
- return error from phy_device_create() if loading module fails

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>