ARM: dts: aspeed-g4: Set spi-max-frequency for all flashes

Set "spi-max-frequency" to 50 MHz for all the flashes under the FMC
controller to ensure the clock frequency is calculated correctly.

Suggested-by: Cédric Le Goater <clg@kaod.org>
Tested-by: Jae Hyun Yoo <quic_jaehyoo@quicinc.com>
Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Link: https://lore.kernel.org/r/20220509175616.1089346-11-clg@kaod.org


Signed-off-by: Joel Stanley <joel@jms.id.au>