powerpc/5200: dts: digsy_mtc.dts: fix rv3029 compatible

The proper compatible for rv3029 is microcrystal,rv3029.

Acked-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>