quota: remove unnecessary oom message

Fixes scripts/checkpatch.pl warning:
WARNING: Possible unnecessary 'out of memory' message

Remove it can help us save a bit of memory. After that, the static
function getdqbuf() becomes unnecessary, get rid of it and instead call
kmalloc() directly.

Link: https://lore.kernel.org/r/20210618014720.1977-2-thunder.leizhen@huawei.com


Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>