[media] davinci: vpbe: fix missing unlock on error in vpbe_initialize()

Add the missing unlock on the error handling path in function
vpbe_initialize().

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Prabhakar Lad <prabhakar.lad@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>