ARM: dts: imx51-ts4800: rename fpga@0 to fpga@0,0

ARM: dts: imx51-ts4800: rename fpga@0 to fpga@0,0

Change node name fpga@0 to fpga@0,0 to fix below CHECK_DTBS warnings:
memory-controller@83fda000 (fsl,imx51-weim): 'fpga@0' does not match any of the regexes: '^.*@[0-7],[0-9a-f]+$', '^pinctrl-[0-9]+$'
        from schema $id: http://devicetree.org/schemas/memory-controllers/fsl/fsl,imx-weim.yam

Signed-off-by: Frank Li <Frank.Li@nxp.com>