net/mlx4_core: clean up srq_res_start_move_to()

Building resource_tracker.o triggers a GCC warning:
    drivers/net/ethernet/mellanox/mlx4/resource_tracker.c: In function 'mlx4_HW2SW_SRQ_wrapper':
    drivers/net/ethernet/mellanox/mlx4/resource_tracker.c:3202:17: warning: 'srq' may be used uninitialized in this function [-Wmaybe-uninitialized]
      atomic_dec(&srq->mtt->ref_count);
                     ^

This is a false positive. But a cleanup of srq_res_start_move_to() can
help GCC here. The code currently uses a switch statement where a plain
if/else would do, since only two of the switch's four cases can ever
occur. Dropping that switch makes the warning go away.

While we're at it, add some missing braces, and convert state to the
correct type.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>