NTB: remove redundant setting of DB valid mask

db_valid_mask is set at two places, once within
amd_init_ntb(), and again within amd_init_dev().
Since amd_init_ntb() is actually called from
amd_init_dev(), setting db_valid_mask from
former does not really make sense. So remove it.
Signed-off-by: Arindam Nath <arindam.nath@amd.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

drivers/ntb/hw/amd/ntb_hw_amd.c

@@ -1056,8 +1056,6 @@ static int amd_init_ntb(struct amd_ntb_dev *ndev)
 		return -EINVAL;
 	}
 
-	ndev->db_valid_mask = BIT_ULL(ndev->db_count) - 1;
-
 	/* Mask event interrupts */
 	writel(ndev->int_mask, mmio + AMD_INTMASK_OFFSET);