pwm: lpss: Fix const qualifier and sparse warnings

Fixes the following warnings reported by the 0-DAY kernel build testing
backend:

   drivers/pwm/pwm-lpss.c: In function 'pwm_lpss_probe_pci':
>> drivers/pwm/pwm-lpss.c:192:2: warning: passing argument 3 of 'pwm_lpss_probe' discards 'const' qualifier from pointer target type [enabled by default]
     lpwm = pwm_lpss_probe(&pdev->dev, &pdev->resource[0], info);
     ^
   drivers/pwm/pwm-lpss.c:130:30: note: expected 'struct pwm_lpss_boardinfo *' but argument is of type 'const struct pwm_lpss_boardinfo *'
    static struct pwm_lpss_chip *pwm_lpss_probe(struct device *dev,
                                 ^
>> drivers/pwm/pwm-lpss.c:143:28: sparse: incorrect type in return expression (different address spaces)
   drivers/pwm/pwm-lpss.c:143:28:    expected struct pwm_lpss_chip *
   drivers/pwm/pwm-lpss.c:143:28:    got void [noderef] <asn:2>*regs
>> drivers/pwm/pwm-lpss.c:192:63: sparse: incorrect type in argument 3 (different modifiers)
   drivers/pwm/pwm-lpss.c:192:63:    expected struct pwm_lpss_boardinfo *info
   drivers/pwm/pwm-lpss.c:192:63:    got struct pwm_lpss_boardinfo const *[assigned] info
   drivers/pwm/pwm-lpss.c: In function 'pwm_lpss_probe_pci':
   drivers/pwm/pwm-lpss.c:192:2: warning: passing argument 3 of 'pwm_lpss_probe' discards 'const' qualifier from pointer target type [enabled by default]
     lpwm = pwm_lpss_probe(&pdev->dev, &pdev->resource[0], info);
     ^
   drivers/pwm/pwm-lpss.c:130:30: note: expected 'struct pwm_lpss_boardinfo *' but argument is of type 'const struct pwm_lpss_boardinfo *'
    static struct pwm_lpss_chip *pwm_lpss_probe(struct device *dev,
                                 ^

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-lpss.c

@@ -129,7 +129,7 @@ static const struct pwm_ops pwm_lpss_ops = {
 
 static struct pwm_lpss_chip *pwm_lpss_probe(struct device *dev,
 					    struct resource *r,
-					    struct pwm_lpss_boardinfo *info)
+					    const struct pwm_lpss_boardinfo *info)
 {
 	struct pwm_lpss_chip *lpwm;
 	int ret;
@@ -140,7 +140,7 @@ static struct pwm_lpss_chip *pwm_lpss_probe(struct device *dev,
 
 	lpwm->regs = devm_ioremap_resource(dev, r);
 	if (IS_ERR(lpwm->regs))
-		return lpwm->regs;
+		return ERR_CAST(lpwm->regs);
 
 	if (info) {
 		lpwm->clk_rate = info->clk_rate;