apm821xx: MBL: band-aid MBL DUO

apm821xx: MBL: band-aid MBL DUO

Takimata reported on the OpenWrt forum in thread [0], that his
MyBook Live Duo wasn't booting OpenWrt 21.02 after upgrading
from the previous OpenWrt 19.07.

The last logged entries on his console

|[    0.531599] sata1-regulator GPIO handle specifies active low - ignored
|[    0.538391] sata0-regulator GPIO handle specifies active low - ignored
|[    0.759791] ata2: SATA link down (SStatus 0 SControl 300)
|[    0.765251] ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
|[    5.909555] ata1.00: qc timeout (cmd 0xec)
|[    5.913656] ata1.00: failed to IDENTIFY (I/O error, err_mask=0x4)
|[    6.231757] ata1: SATA link down (SStatus 0 SControl 300)

This extract clearly showed that the HDD on which OpenWrt is installed,
simply disappeared after the SATA power regulators had been initialized.

Since the device-tree regulators haven't changed since the OpenWrt 19.07
days this will require further investigation on the snapshot/master/trunk
branch.

For the time being, it was requested to just delete the nodes so,
the device will boot again. Which unfortunately,  will have to wait
until 21.02.1 is released.

He also confirmed that the My Book Live Single wasn't affected.
It works with or without this change.

[0] <https://forum.openwrt.org/t/21-02-0-and-snapshot-fail-to-boot-on-my-book-live-duo/106585>

Reported-by: Takimata (forum.openwrt.org/u/takimata)
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>