[media] gsc-core: Remove useless test

drivers/media/platform/exynos-gsc/gsc-core.c: In function 'gsc_probe':
drivers/media/platform/exynos-gsc/gsc-core.c:1089:2: warning: comparison is alw
ays false due to limited range of data type [-Wtype-limits]
  if (gsc->id < 0 || gsc->id >= drv_data->num_entities) {
  ^

gsc->id is declared as u16, so it should always be a positive
value.

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