[S2IO]: Fixed memory leak when MSI-X vector allocation fails

- Fixed memory leak by freeing MSI-X local entry memories when vector allocation
fails in s2io_add_isr.
- Added two utility functions remove_msix_isr and remove_inta_isr to eliminate
code duplication.
- Incorporated following review comments from Jeff
        - Removed redundant stats->mem_freed and synchronize_irq call
        - do_rem_msix_isr is renamed as remove_msix_isr
        - do_rem_inta_isr is renamed as remove_inta_isr

Signed-off-by: Sreenivasa Honnur <sreenivasa.honnur@neterion.com>
Signed-off-by: David S. Miller <davem@davemloft.net>