sdhci_pci0_slot0: Controller Timeout

Running most recent CURRENT (r296023) on an Intel NUC with a Intel Celeron 3050
CPU, booting off a SD card, the box complains about a SDHCI controler timeout
with

sdhci_pci0_slot0: Controller Timeout

followed by a register dump. Thiss takes up to two minutes, then the box boots
through.

The SD card slot reader (built-in) seems to reside at slot1, so I guess probing
the slot0 followed by the error shown above is not a real bug or error.

If not an error, is there a way to avoid/skip probing slot0 or shorten the
probing attempts?

Thanks in advance,

Oliver