This fixes several warnings like:
	drivers/spi/spi-mpc512x-psc.c: In function 'mpc512x_psc_spi_prep_xfer_hw':
	arch/powerpc/include/asm/io.h:163:2: warning: '__ret' may be used uninitialized in this function [-Wmaybe-uninitialized]
introduced in commit 
8bf960985dfc for some build configurations.
Fixes: 8bf960985dfc ("spi: mpc512x-psc: add support for Freescale MPC5125")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>
  * MPC5121 (which uses a struct mpc52xx_psc) and MPC5125 (using mpc5125_psc).
  */
 #define psc_addr(mps, regname) ({                                      \
-       void *__ret;                                                    \
-       switch(mps->type) {                                             \
+       void *__ret = NULL;                                             \
+       switch (mps->type) {                                            \
        case TYPE_MPC5121: {                                            \
                        struct mpc52xx_psc __iomem *psc = mps->psc;     \
                        __ret = &psc->regname;                          \