spi/s3c64xx: Add missing pm_runtime_put on setup fail

pm_runtime_put() wasn't called if clock rate could not be set up in
s3c64xx_spi_setup() leading to invalid count of device pm_runtime usage.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mark Brown <broonie@linaro.org>