media: s5p-mfc: Fix encoder menu controls initialization

This patch fixes the menu_skip_mask field initialization and
addresses a following issue found by the SVACE static analysis:

* NO_EFFECT.SELF: assignment to self in expression 'cfg.menu_skip_mask = cfg.menu_skip_mask'
  No effect at drivers/media/platform/s5p-mfc/s5p_mfc_enc.c:2083

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>