media: staging: media: atomisp: fix stack overflow in init_pipe_defaults()

When building with clang, multiple copies of the structures to be
initialized are passed around on the stack and copied locally, using an
insane amount of stack space:

drivers/staging/media/atomisp/pci/sh_css.c:2371:1: error: stack frame size of 26864 bytes in function 'create_pipe' [-Werror,-Wframe-larger-than=]

Use constantly-allocated variables plus an explicit memcpy()
to avoid that.

Co-authored-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Fixes: 6dc9a256 ("media: atomisp: convert default struct values to use compound-literals with designated initializers")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>