Staging: crystalhd: prefer pr_warn to printk(KERN_WARNING)

Fix warning issue by using pr_err instead of printk

Signed-off-by: Georgiana Rodica Chelu <georgiana.chelu93@gmail.com>
Reviewed-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>