spi: stm32: renaming of spi_master into spi_controller

Preparing introduction of SPI device, rename the spi_master structure
into spi_controller. This doesn't have any functional impact since
spi_master was already a macro for spi_controller.
Referring now to ctrl instead of master since the spi_controller
structure might not be used as a master controller only.

Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Link: https://lore.kernel.org/r/20230615075815.310261-2-valentin.caron@foss.st.com
Signed-off-by: Mark Brown <broonie@kernel.org>