[media] media: usb: cpia2: Use kmemdup instead of kmalloc and memcpy

When some other buffer is immediately copied into allocated region.
Replace calls to kmalloc followed by a memcpy with a direct
call to kmemdup.

Signed-off-by: Shyam Saini <mayhs11saini@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>