spi: cs42l43: Correct SPI root clock speed

The root clock is actually 49.152MHz not 40MHz, as it is derived from
the primary audio clock, update the driver to match. This error can
cause the actual clock rate to be higher than the requested clock rate
on the SPI bus.

Fixes: ef75e767

 ("spi: cs42l43: Add SPI controller support")
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://msgid.link/r/20240604131704.3227500-1-ckeepax@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>