fixup! drivers/periph_api: change API of spi_acquire (from RIOT-OS#15904

)

drivers/include/periph/spi.h

@@ -372,15 +372,13 @@ uint32_t spi_get_freq(spi_clk_t clk);
  * @param[in]   mode    mode to use for the new transaction
  * @param[in]   clk     opaque clock configuration obtain from @ref spi_get_clk
  *
- * @return  The actually used clock frequency in Hz
- *
  * @pre     All parameters are valid and supported, otherwise an assertion blows
  *          up (if assertions are enabled).
  *
  * @post    Exclusive access to the SPI bus is guaranteed until @ref spi_release
  *          is called.
  */
-uint32_t spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk);
+void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk);
 
 /**
  * @brief   Finish an ongoing SPI transaction by releasing the given SPI bus