RDMA/uverbs: Refactor flow_resources_alloc() function

Simplify the flow_resources_alloc() function call by reducing
number of goto statements.

Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>