client: Fix caps_ref[c]<0 assert

client: Fix caps_ref[c]<0 assert

When libcephfs aio tests (src/test/client) are run
with objectcacher disabled (ceph_test_client --client_oc=false),
the TestClient.LlreadvLlwritev fails and core dumps. The client
hits the assert 'caps_ref[c]<0'.

This patch fixes the same. There is no need to give out cap_ref
and take it again between multiple read because of short reads.
In some cases, the get_caps used to fail in C_Read_Sync_NonBlocking::finish
causing cap_ref to go negative when put_cap_ref is done at last in
C_Read_Finish::finish_io

Fixes: https://tracker.ceph.com/issues/68308
Signed-off-by: Kotresh HR <khiremat@redhat.com>