Staging: media: davinci_vpfe: Fix preferred form of passing a size

Fix preferred form of passing a size of a struct to improve readability
and eradicate an opportunity for a bug when the pointer variable type is
changed but the corresponding sizeof that is passed to a memory
allocator is not.

Signed-off-by: Madhumitha Prabakaran <madhumithabiw@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>