Staging: iio: replace pr_err with dev_err

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>