[media] s5p-mfc: Remove unused s5p_mfc_get_decoded_status_v6() function

This patch fixes following compilation warning:
  CC [M]  drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.o
drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.c:1733:12: warning: ‘s5p_mfc_get_decoded_status_v6’ defined but not used
It assigns existing but not used s5p_mfc_get_dec_status_v6() function to the
get_dec_status callback. It seems the get_dec_status callback is not used
anyway, as there is no corresponding s5p_mfc_hw_call().

Signed-off-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>