[media] exynos-gsc: send valid m2m ctx to gsc_m2m_job_finish

gsc_m2m_job_finish() has to be called with the m2m context for the necessary
cleanup while resume. But currently gsc_m2m_job_finish() always passes m2m
context as NULL.
This patch preserves the context before making it null, for necessary cleanup.
Use gsc_m2m_opened() instead gsc_m2m_active() in gsc_resume().

Signed-off-by: Shaik Ameer Basha <shaik.ameer@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>