media: staging: media: davinci_vpfe: use __func__ for function names

Checkpatch reported warnings for use of embedded function names.
Use __func__ instead of embedded function names.

[mchehab+samsung@kernel.org: rebased on the top of upstream]
Signed-off-by: Diwakar Sharma <sharmalxmail@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>