V4L/DVB (4997): Bttv: delete duplicated ioremap()

ioremap() is called twice to same resource.
The returen value of first one is not error-checked.
second one is complely ignored.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>