variants: arduino_nano_33_iot: describe unit address in hex

[soburi]

Fix this warnings

unit address and first address in 'reg' (0xa) don't match for /soc/adc@42004000/channel@10
unit address and first address in 'reg' (0xb) don't match for /soc/adc@42004000/channel@11
unit address and first address in 'reg' (0x12) don't match for /soc/adc@42004000/channel@18
unit address and first address in 'reg' (0x13) don't match for /soc/adc@42004000/channel@19

unit address and first address in 'reg' (0x6a) don't match for /soc/sercom@42001800/atecc608a@15

may be problem in boards/arm/arduino_nano_33_iot/arduino_nano_33_iot.dts

[DhruvaG2000]

Cherry-picked these changes on top of PR#60 , and the warnings do go away.
hence, LGTM.

[DhruvaG2000]

Please rebase #60 now that this PR is being merged in upstream main.
Thanks!