pwm: imx-tpm: Use a single line for error message

There is no need to split the dev_err() call in three lines.

Use a single line to improve readability.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>