ceph: fix memory leak in ceph_direct_read_write()

In the Linux kernel, the following vulnerability has been resolved:

ceph: fix memory leak in ceph_direct_read_write()

The bvecs array which is allocated in iter_get_bvecs_alloc() is leaked

and pages remain pinned if ceph_alloc_sparse_ext_map() fails.

There is no need to delay the allocation of sparse_ext map until after

the bvecs array is set up, so fix this by moving sparse_ext allocation

a bit earlier. Also, make a similar adjustment in __ceph_sync_read()

for consistency (a leak of the same kind in __ceph_sync_read() has been

addressed differently).