arm64: dts: mt7622: specify the number of DMA requests

arm64: dts: mt7622: specify the number of DMA requests

The MT7622 device tree never bothered to specify the number of virtual DMA
channels for the HSDMA controller, always falling back to the default value of
3. Make this value explicit, in order to avoid the following dmesg notification:

mtk_hsdma 1b007000.dma-controller: Using 3 as missing dma-requests property

Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>
Link: https://lore.kernel.org/r/20220429084225.298213-1-rsalvaterra@gmail.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>