pvr: zero-initialize variable

Because of incomplete codepaths further down in this function, we end up
trying to use this variable without initialization. Let's initialize it
to zero, just to keep the compiler happy.

This avoids a compile-time warning, which would get treated as an error
on CI.

Reviewed-by: Karmjit Mahil <Karmjit.Mahil@imgtec.com>
Part-of: <!15525>