net: dsa: mv88e6xxx: error handling for serdes_power functions

net: dsa: mv88e6xxx: error handling for serdes_power functions

commit 0416e7af2369b0d12a28dea8d30b104df9a6953d upstream.

Added default case to handle undefined cmode scenario in
mv88e6393x_serdes_power() and mv88e6393x_serdes_power() methods.

Addresses-Coverity: 1494644 ("Uninitialized scalar variable")
Fixes: 21635d9203e1c (net: dsa: mv88e6xxx: Fix application of erratum 4.8 for 88E6393X)
Reviewed-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Ameer Hamza <amhamza.mgc@gmail.com>
Link: https://lore.kernel.org/r/20211209041552.9810-1-amhamza.mgc@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>