[media] stv090x: Some whitespace cleanups

While writing changeset fdf1bc9f

, I noticed some checkpatch
complains about the CodingStyle for function parameters. So,
clean them.

While here, also removes uneeded "extern" from function prototype.

No functional changes.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>