dt-bindings: dma: mpfs-fpga-dma: remove redundant quoting causing validation errors

commit c1555d5ed991a937d1a3346dbd354daeb944bd92 from
https://github.com/linux4microchip/linux.git

 linux-6.6-mchp+fpga

Fix:
../Documentation/devicetree/bindings/dma/microchip,mpfs-fpga-dma.yaml:13:11: [error] string value is redundantly quoted with any quotes (quoted-strings)

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: harish h <harish.h@windriver.com>