net/rds: Fix 'ib_evt_handler_call' element in 'rds_ib_stat_names'

All entries in 'rds_ib_stat_names' are stringified versions
of the corresponding "struct rds_ib_statistics" element
without the "s_"-prefix.

Fix entry 'ib_evt_handler_call' to do the same.

Fixes: f4f943c9

 ("RDS: IB: ack more receive completions to improve performance")
Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>