ata: ahci_mvebu: Fix wrongly set base address for the MBus window setting

ata: ahci_mvebu: Fix wrongly set base address for the MBus window setting

According to the Armada 38x datasheet, the window base address
registers value is set in bits [31:4] of the register and corresponds
to the transaction address bits [47:20].

Therefore, the 32bit base address value should be shifted right by
20bits and left by 4bits, resulting in 16 bit shift right.

The bug as not been noticed yet because if the memory available on
the platform is less than 2GB, then the base address is zero.

[gregory.clement@free-electrons.com: add extra-explanation]

Fixes: 6688b12e20e (ata: ahci_mvebu: new driver for Marvell Armada 380
AHCI interfaces)
Signed-off-by: Nadav Haklai <nadavh@marvell.com>
Reviewed-by: Omri Itach <omrii@marvell.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>