spi: microchip-core: fix init function not setting the master and motorola modes

[ Upstream commit 3a5e76283672efddf47cea39ccfe9f5735cc91d5 ]

mchp_corespi_init() reads the CONTROL register, sets the master and
motorola bits, but doesn't write the value back to the register. The
function also doesn't ensure the controller is disabled at the start,
which may present a problem if the controller was used by an
earlier boot stage as some settings (including the mode) can only be
modified while the controller is disabled.

Fixes: 9ac8d176

 ("spi: add support for microchip fpga spi controllers")
Signed-off-by: Steve Wilkins <steve.wilkins@raymarine.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20240715-designing-thus-05f7c26e1da7@wendy
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>