r8169: replace BUG_ON with WARN in _rtl_eri_write

Use WARN here to avoid stopping the system. In addition print the addr
and mask values that triggered the warning.

v2:
- return on WARN to avoid an invalid register write

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>