IB/iser: Remove dead code in fmr_pool alloc/free

In the past the we always tried to allocate an fmr_pool
and if it failed on ENOSYS (not supported) then we continued
with dma mr. This is not the case anymore and if we tried to
allocate an fmr_pool then it is supported and we expect to succeed.

Also, the check if fmr_pool is allocated when free is called is
redundant as well as we are guaranteed it exists.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>