[media] bttv-driver: fix two warnings

drivers/media/pci/bt8xx/bttv-driver.c:308:3: warning: initialized field overwritten [-Woverride-init]
drivers/media/pci/bt8xx/bttv-driver.c:308:3: warning: (near initialization for 'bttv_tvnorms[0].cropcap.bounds.height') [-Woverride-init]
drivers/media/pci/bt8xx/bttv-driver.c: In function 'bttv_remove':
drivers/media/pci/bt8xx/bttv-driver.c:4467:29: warning: suggest braces around empty body in an 'if' statement [-Wempty-body]

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