[media] ivtv-i2c: Fix two warnings

Fix two gcc warnings:

drivers/media/video/ivtv/ivtv-i2c.c:170: warning: cast from pointer to integer of different size
drivers/media/video/ivtv/ivtv-i2c.c:171: warning: cast from pointer to integer of different size
$ gcc --version
gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-48)

They seem bogus, but, as the original code also has problems with
LE/BE, just change its implementation to be clear.

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