media: davinci: do a couple of checkpatch cleanups

- Delete an error message for a failed memory allocation
  in init_vpbe_layer();

- Replace the specification of data structures by pointer dereferences
  as the parameter for the operator "sizeof" to make the corresponding
  size determination a bit safer according to the Linux coding style
  convention;

- media: DaVinci-VPBE-Display: Improve a size determination in two
  functions

- Adjust 12 checks for null pointers

Those issues were pointed by checkpatch.pl and Coccinelle.

[mchehab@s-opensource.com: fold three cleanup patches into one]
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>