RDMA/nes: Free IRQ before killing tasklet

Move the free_irq() call in nes_remove() to before the tasklet_kill();
otherwise there is a window after tasklet_kill() where a new interrupt
can be handled and reschedule the tasklet, leading to a use-after-free
crash.

Cc: <stable@kernel.org>
Signed-off-by: Roland Dreier <rolandd@cisco.com>