spi: s3c64xx: use error code from clk_prepare_enable()

If clk_prepare_enable() fails do not return -EBUSY but use the
value provided by the function itself.

Suggested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Andi Shyti <andi.shyti@samsung.com>
Reviewed-by: Michael Turquette <mturquette@baylibre.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>