fs/9p: fix the cache always being enabled on files with qid flags

fs/9p: fix the cache always being enabled on files with qid flags

I'm not sure why this check was ever here. After updating to 6.6 I
suddenly found caching had been turned on by default and neither
cache=none nor the new directio would turn it off. After walking through
the new code very manually I realized that it's because the caching has
to be, in effect, turned off explicitly by setting P9L_DIRECT and
whenever a file has a flag, in my case QTAPPEND, it doesn't get set.

Setting aside QTDIR which seems to ignore the new fid->mode entirely,
the rest of these either should be subject to the same cache rules as
every other QTFILE or perhaps very explicitly not cached in the case of
QTAUTH.

Signed-off-by: Joakim Sindholt <opensource@zhasha.com>
Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>