V4L/DVB (7110): Trivial printf warning fix (radio-si470)

Thanks to  Darren Salt <linux@youmustbejoking.demon.co.uk> for pointing this
issue.

Signed-off-by: Tobias Lorenz <tobias.lorenz@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>