[media] exynos-gsc: Rearrange error messages for valid prints

In case of clk_prepare failure, the function gsc_clk_get also prints
"failed to get clock" which is not correct. Hence move the error
messages to their respective blocks. While at it, also renamed the labels
meaningfully.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>