r8169: avoid duplicated messages if loading firmware fails and switch to warn level

In case of a problem with firmware loading we inform at the driver level,
in addition the firmware load code itself issues warnings. Therefore
switch to firmware_request_nowarn() to avoid duplicated error messages.
In addition switch to warn level because the firmware is optional and
typically just fixes compatibility issues.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Message-ID: <d9c5094c-89a6-40e2-b5fe-8df7df4624ef@gmail.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>