Ext4Pkg: Fix incorrect checksum metadata feature check

We need to check EXT4_FEATURE_RO_COMPAT_METADATA_CSUM in the
FeatureRoCompat field instead of FeaturesCompat. The proper way to do
this is to use macro EXT4_HAS_METADATA_CSUM. 
Also, replace the EXT4_FEATURE_INCOMPAT_CSUM_SEED check with predefined
macro EXT4_HAS_INCOMPAT

Cc: Marvin Häuser <mhaeuser@posteo.de>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
Cc: Vitaly Cheptsov <vit9696@protonmail.com>
Fixes: d9ceedca ("Ext4Pkg: Add Ext4Dxe driver.")
Signed-off-by: Savva Mitrofanov <savvamtr@gmail.com>
Reviewed-by: Pedro Falcato <pedro.falcato@gmail.com>
Reviewed-by: Marvin Häuser <mhaeuser@posteo.de>