powerpc/ps3: remove orphan declarations from ps3av.h

Remove the following orphan declarations from ps3av.h:
1. ps3av_dev_open()
2. ps3av_dev_close()

They have been removed since commit 13a5e30c ("[POWERPC] PS3:
Rework AV settings driver"), so remove them.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Acked-by: Geoff Levand <geoff@infradead.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220913075029.682327-9-cuigaosheng1@huawei.com