V4L/DVB (3312): FIX: Multiple usage of VP7045-based devices

Reassigning function pointers in a static led to infinite loops when using
multiple VP7045-based device at the same time on one system. Using kmalloc'd
copies for reassignments is better.

Signed-off-by: Patrick Boettcher <pb@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>