misc/ep93xx_pwm: use managed device resources

Use managed device resources to clean up the probe/remove.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Ryan Mallon <rmallon@gmail.com>
Cc: Matthieu Crapet <mcrapet@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>