bnxt_en: map CAG_REG_LEGACY_INT_STATUS_MASK to GRC window #4

In order to use offset 0x4014 for reading CAG interrupt status,
the actual CAG register must be mapped to GRC bar0 window #4.
Otherwise, the driver is reading garbage. This patch corrects
this issue.

Signed-off-by: Jeffrey Huang <huangjw@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>