media: atomisp: don't pass a pointer to a local variable

As warned by gcc 12.1:

	drivers/staging/media/atomisp/pci/runtime/rmgr/src/rmgr_vbuf.c: In function 'ia_css_rmgr_acq_vbuf':
	drivers/staging/media/atomisp/pci/runtime/rmgr/src/rmgr_vbuf.c:275:33: error: storing the address of local variable 'h' in '*handle' [-Werror=dangling-pointer=]
	  275 |                         *handle = &h;
	      |                         ~~~~~~~~^~~~
	drivers/staging/media/atomisp/pci/runtime/rmgr/src/rmgr_vbuf.c:257:40: note: 'h' declared here
	  257 |         struct ia_css_rmgr_vbuf_handle h;
	      |                                        ^
	drivers/staging/media/atomisp/pci/runtime/rmgr/src/rmgr_vbuf.c:257:40: note: 'handle' declared here
	cc1: all warnings being treated as errors

The logic uses a temporary struct to update the handler, but,
instead of copying the value to the pointer sent by the caller, it
replaces it with the content with a local variable. That's wrong, and
may lead the caller to use a weird value.

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>