rgw/rgw_op: fix indentation warning

rgw/rgw_op: fix indentation warning

/home/sage/src/ceph2/src/rgw/rgw_op.cc: In member function ‘virtual void RGWDeleteObjTags::execute()’:
/home/sage/src/ceph2/src/rgw/rgw_op.cc:777:3: warning: this ‘if’ clause does not guard... [-Wmisleading-indentation]
   if (s->object.empty())
   ^~
/home/sage/src/ceph2/src/rgw/rgw_op.cc:780:5: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the ‘if’
     rgw_obj obj;
     ^~~~~~~

Signed-off-by: Sage Weil <sage@redhat.com>