IB/ipath: Fix sparse warning about pointer signedness

There's no reason for the third parameter of ipath_count_units() to be
a u32 *, so change it to be an int * instead.  This fixes the sparse
warning:

    drivers/infiniband/hw/ipath/ipath_file_ops.c:1654:47: warning: incorrect type in argument 3 (different signedness)
    drivers/infiniband/hw/ipath/ipath_file_ops.c:1654:47:    expected unsigned int [usertype] *maxportsp
    drivers/infiniband/hw/ipath/ipath_file_ops.c:1654:47:    got int *<noident>

Signed-off-by: Arthur Jones <arthur.jones@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>