Fix variable type warning

Fix variable type warning

Bruce reports:

With 2.0.13 on FreeBSD there's also a warning from client.c:

client.c:24:18: warning: field 'eta' with variable sized type 'struct
jobs_eta' not at the end of a struct or class is a GNU extension [-Wgnu]
         struct jobs_eta eta;

Re-order ->eta and ->pending.

Signed-off-by: Jens Axboe <axboe@kernel.dk>