Staging: speakup: Use pr_warn() defined in <linux/printk.h>.

Staging: speakup: Use pr_warn() defined in <linux/printk.h>.

Dropping a user-defined pr_warn() and using the kernel
message printing functions implemented in <linux/printk.h>.

Since both have the same functionality, using the standard
kernel functions is better.

Signed-off-by: Sam Muhammed <jane.pnx9@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Link: https://lore.kernel.org/r/20200322143322.29098-1-jane.pnx9@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>