spi: microchip-core: Remove the unused function mchp_corespi_enable()

The function mchp_corespi_enable() is defined in the spi-microchip-core.c
file, but not called elsewhere, so delete this unused function.

drivers/spi/spi-microchip-core.c:122:20: warning: unused function 'mchp_corespi_enable'.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=2418
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20221017092141.9789-1-jiapeng.chong@linux.alibaba.com
Signed-off-by: Mark Brown <broonie@kernel.org>