fix: bananapi-m2-zero spi only

[MSzturc]

No description provided.

[KwadFan]

First of all, thank you for your contribution.
Could you please explain why are you inverting the logic and why you are using the logic for "SPI only" to enable UART?
Did you set the config right? Because, if you set

## BananaPi M2 Zero specific
### Disable OTG Serial Interface? (true/false)
[[ -n "$ARMBIAN_CONFIG_BPI2ZERO_OTG_SERIAL" ]] || ARMBIAN_CONFIG_BPI2ZERO_OTG_SERIAL="true"
[[ -n "$ARMBIAN_CONFIG_BPI2ZERO_ENABLE_UART3" ]] || ARMBIAN_CONFIG_BPI2ZERO_ENABLE_UART3="true"
[[ -n "$ARMBIAN_CONFIG_BPI2ZERO_ENABLE_SPI" ]] || ARMBIAN_CONFIG_BPI2ZERO_ENABLE_SPI="false"

it will trigger

MainsailOS/src/modules/armbian/start_chroot_script

Line 163 in 0d951e4

echo "overlays=uart3" >> "${ARMBIAN_CONFIG_TXT_FILE}"

instead, which as I am not mistaken here is, what you try to archive.

Furthermore I want to point out that the BananaPI M2 will not be published, this is only for internal testing and was once created to help out the Desingner of "the100" which never got to a point to be "finished".
So, I am unsure if we need those changes and I will discuss this internally.

Regards Kwad