doc-rst: linux_tv: don't simplify VIDIOC_G_foo references

As VIDIOC_G_foo is the reference used for VIDIOC_S_foo and
VIDIOC_TRY_foo, we need to explicitly name the reference, as
otherwise, it will mention the three ioctls altogether, with
is not what we want.

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