This patch marks the function _c4iw_write_mem_dma() as static
because it is not used outside this file, which fixes the warning:

    drivers/infiniband/hw/cxgb4/mem.c:176:5: warning: no previous prototype for ‘_c4iw_write_mem_dma’ [-Wmissing-prototypes]
Signed-off-by: NRashika Kheria <rashika.kheria@gmail.com>
Acked-by: NSteve Wise <swise@opengridcomputing.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
Signed-off-by: NRoland Dreier <roland@purestorage.com>