spi: clps711x: Provide label argument for devm_gpio_request

The label argument was removed by commit 98984796


spi: clps711x: Use devm_gpio_request(), add it back.
This makes it easier to know the gpio usage in /sys/kernel/debug/gpio.

Also remove unnecessary gpio_is_valid() checking, devm_gpio_request() returns
error if the requested gpio is invalid.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>