osd: guard checks for writes
osd: guard checks for writes

fa722de6708d3e92037df6289cc29ece12c8ea66 moved these checks, and
accidentally removed the may_write() guard. This caused reading from
snapshots to fail.

Signed-off-by: Josh Durgin <51652c783f70f5b272ebd02f1fd20d3af7a2449f@dreamhost.com>

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph