Staging: iio: replace pr_err with dev_err

This patch replace pr_err with dev_err, when appropriate device structre
is found.
Issue found using the following Coccinelle script:

@r exists@
identifier f, s, i;
position p;
@@

f(...,struct s *i,...) {
<+...
when != i == NULL
pr_err@p(...);
...+>
}

@rr@
identifier r.s, fld;
@@

struct s {
	...
	struct device *fld;
	...
};

@@
identifier r.i, rr.fld;
position r.p;
@@
-pr_err@p
+dev_err
   (
+ i->fld,
...)
Signed-off-by: Haneen Mohammed <hamohammed.sa@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/resolver/ad2s1210.c

@@ -214,7 +214,7 @@ static ssize_t ad2s1210_store_fclkin(struct device *dev,
 	if (ret)
 		return ret;
 	if (fclkin < AD2S1210_MIN_CLKIN || fclkin > AD2S1210_MAX_CLKIN) {
-		pr_err("ad2s1210: fclkin out of range\n");
+		dev_err(dev, "ad2s1210: fclkin out of range\n");
 		return -EINVAL;
 	}
 
@@ -252,7 +252,8 @@ static ssize_t ad2s1210_store_fexcit(struct device *dev,
 	if (ret < 0)
 		return ret;
 	if (fexcit < AD2S1210_MIN_EXCIT || fexcit > AD2S1210_MAX_EXCIT) {
-		pr_err("ad2s1210: excitation frequency out of range\n");
+		dev_err(dev,
+			"ad2s1210: excitation frequency out of range\n");
 		return -EINVAL;
 	}
 	mutex_lock(&st->lock);
@@ -307,7 +308,8 @@ static ssize_t ad2s1210_store_control(struct device *dev,
 		goto error_ret;
 	if (ret & AD2S1210_MSB_IS_HIGH) {
 		ret = -EIO;
-		pr_err("ad2s1210: write control register fail\n");
+		dev_err(dev,
+			"ad2s1210: write control register fail\n");
 		goto error_ret;
 	}
 	st->resolution
@@ -346,7 +348,7 @@ static ssize_t ad2s1210_store_resolution(struct device *dev,
 
 	ret = kstrtou8(buf, 10, &udata);
 	if (ret || udata < 10 || udata > 16) {
-		pr_err("ad2s1210: resolution out of range\n");
+		dev_err(dev, "ad2s1210: resolution out of range\n");
 		return -EINVAL;
 	}
 	mutex_lock(&st->lock);
@@ -368,7 +370,7 @@ static ssize_t ad2s1210_store_resolution(struct device *dev,
 	data = ret;
 	if (data & AD2S1210_MSB_IS_HIGH) {
 		ret = -EIO;
-		pr_err("ad2s1210: setting resolution fail\n");
+		dev_err(dev, "ad2s1210: setting resolution fail\n");
 		goto error_ret;
 	}
 	st->resolution