ntb: initialize max_mw for Atom before using it

Commit ab760a0c (ntb: Adding split BAR support for Haswell platforms)
changed ntb_device's mw from a fixed-size array into a pointer that is
allocated based on limits.max_mw; however, on Atom platforms, max_mw
is not initialized until ntb_device_setup(), which happens after the
allocation.

Fill out max_mw in ntb_atom_detect() to match ntb_xeon_detect(); this
happens before the use of max_mw in the ndev->mw allocation.

Fixes a null pointer dereference on Atom platforms with ntb hardware.

v2: fix typo (mw_max should be max_mw)
Signed-off-by: NDaniel Verkamp <daniel.verkamp@intel.com>
Acked-by: NDave Jiang <dave.jiang@intel.com>
Signed-off-by: NJon Mason <jdmason@kudzu.us>

drivers/ntb/ntb_hw.c

@@ -1660,6 +1660,7 @@ static int ntb_atom_detect(struct ntb_device *ndev)
 	u32 ppd;
 
 	ndev->hw_type = BWD_HW;
+	ndev->limits.max_mw = BWD_MAX_MW;
 
 	rc = pci_read_config_dword(ndev->pdev, NTB_PPD_OFFSET, &ppd);
 	if (rc)