spi: Update reference to struct spi_controller

struct spi_master has been renamed to struct spi_controller. Update the
reference in spi.rst to make it clickable again.

Fixes: 8caab75f ("spi: Generalize SPI "master" to "controller"")
Signed-off-by: NJonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20221101173252.1069294-1-j.neuschaefer@gmx.netSigned-off-by: NMark Brown <broonie@kernel.org>

Documentation/driver-api/spi.rst

@@ -25,8 +25,8 @@ hardware, which may be as simple as a set of GPIO pins or as complex as
 a pair of FIFOs connected to dual DMA engines on the other side of the
 SPI shift register (maximizing throughput). Such drivers bridge between
 whatever bus they sit on (often the platform bus) and SPI, and expose
-the SPI side of their device as a :c:type:`struct spi_master
-<spi_master>`. SPI devices are children of that master,
+the SPI side of their device as a :c:type:`struct spi_controller
+<spi_controller>`. SPI devices are children of that master,
 represented as a :c:type:`struct spi_device <spi_device>` and
 manufactured from :c:type:`struct spi_board_info
 <spi_board_info>` descriptors which are usually provided by