filesetup: don't print non-debug error on native fallocate failure

filesetup: don't print non-debug error on native fallocate failure

We expect this to fail in cases where it isn't available, so don't
clutter the standard/error output with it.

Also ensure that native_fallocate() returns true/false, since it's
a bool function. Just a cleanup, no functional change there.

Fixes: 2c3e17be4c7c ("filesetup: add native fallocate")
Signed-off-by: Jens Axboe <axboe@kernel.dk>