net: dsa: mv88e6xxx: use mv88e6185_g1_vtu_loadpurge() for the 6250

Apart from the mask used to get the high bits of the fid,
mv88e6185_g1_vtu_loadpurge() and mv88e6250_g1_vtu_loadpurge() are
identical. Since the entry->fid passed in should never exceed the
number of databases, we can simply use the former as-is as replacement
for the latter.

Suggested-by: Tobias Waldekranz <tobias@waldekranz.com>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>