enetc: Fix unused var build warning for CONFIG_OF

enetc: Fix unused var build warning for CONFIG_OF

When CONFIG_OF is disabled, there is a harmless warning about
an unused variable:

enetc_pf.c: In function 'enetc_phylink_create':
enetc_pf.c:981:17: error: unused variable 'dev' [-Werror=unused-variable]

Slightly rearrange the code to pass around the of_node as a
function argument, which avoids the problem without hurting
readability.

Fixes: 71b77a7a27a3 ("enetc: Migrate to PHYLINK and PCS_LYNX")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Link: https://lore.kernel.org/r/20201204120800.17193-1-claudiu.manoil@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>