[media] g2d: remove unused var

drivers/media/platform/s5p-g2d/g2d.c: In function 'job_abort':
drivers/media/platform/s5p-g2d/g2d.c:493:6: warning: variable 'ret' set but not used [-Wunused-but-set-variable]
  int ret;
      ^

The job_abort function returns void. No sense to get the
returned argument, if this won't be used.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>