spi: spi-axi-spi-engine: Access register after clock initialization

Move register access after clock initialization.
Clock "s_axi_aclk" is needed for register access. Without the clock running
AXI bus hangs and causes kernel freeze.

Signed-off-by: Rafał Hibner <rafal.hibner@secom.com.pl>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Cc: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20200409155621.12174-1-rafal.hibner@secom.com.pl


Signed-off-by: Mark Brown <broonie@kernel.org>