memory: samsung: exynos5422-dmc: Do not ignore return code of regmap_read()

Check for regmap_read() return code before using the read value in
following write in exynos5_switch_timing_regs().  Pass reading error
code to the callers.

This does not introduce proper error handling for such failed reads (and
obviously regmap_write() error is still ignored) because the driver
ignored this in all places.  Therefor it only fixes reported issue while
matching current driver coding style:

       drivers/memory/samsung/exynos5422-dmc.c: In function 'exynos5_switch_timing_regs':
    >> drivers/memory/samsung/exynos5422-dmc.c:216:6: warning: variable 'ret' set but not used [-Wunused-but-set-variable]
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

drivers/memory/samsung/exynos5422-dmc.c

@@ -270,12 +270,14 @@ static int find_target_freq_idx(struct exynos5_dmc *dmc,
  * This function switches between these banks according to the
  * currently used clock source.
  */
-static void exynos5_switch_timing_regs(struct exynos5_dmc *dmc, bool set)
+static int exynos5_switch_timing_regs(struct exynos5_dmc *dmc, bool set)
 {
 	unsigned int reg;
 	int ret;
 
 	ret = regmap_read(dmc->clk_regmap, CDREX_LPDDR3PHY_CON3, &reg);
+	if (ret)
+		return ret;
 
 	if (set)
 		reg |= EXYNOS5_TIMING_SET_SWI;
@@ -283,6 +285,8 @@ static void exynos5_switch_timing_regs(struct exynos5_dmc *dmc, bool set)
 		reg &= ~EXYNOS5_TIMING_SET_SWI;
 
 	regmap_write(dmc->clk_regmap, CDREX_LPDDR3PHY_CON3, reg);
+
+	return 0;
 }
 
 /**
@@ -516,7 +520,7 @@ exynos5_dmc_switch_to_bypass_configuration(struct exynos5_dmc *dmc,
 	/*
 	 * Delays are long enough, so use them for the new coming clock.
 	 */
-	exynos5_switch_timing_regs(dmc, USE_MX_MSPLL_TIMINGS);
+	ret = exynos5_switch_timing_regs(dmc, USE_MX_MSPLL_TIMINGS);
 
 	return ret;
 }
@@ -577,7 +581,9 @@ exynos5_dmc_change_freq_and_volt(struct exynos5_dmc *dmc,
 
 	clk_set_rate(dmc->fout_bpll, target_rate);
 
-	exynos5_switch_timing_regs(dmc, USE_BPLL_TIMINGS);
+	ret = exynos5_switch_timing_regs(dmc, USE_BPLL_TIMINGS);
+	if (ret)
+		goto disable_clocks;
 
 	ret = clk_set_parent(dmc->mout_mclk_cdrex, dmc->mout_bpll);
 	if (ret)