crypto: ccp - Fix snp_filter_reserved_mem_regions() off-by-one

crypto: ccp - Fix snp_filter_reserved_mem_regions() off-by-one

Sashiko notes:

> regarding the bounds check in snp_filter_reserved_mem_regions()
> called via walk_iomem_res_desc(): does the check
> if ((range_list->num_elements * 16 + 8) > PAGE_SIZE)
> allow an off-by-one heap buffer overflow?
>
> If range_list->num_elements is 255, 255 * 16 + 8 = 4088, which is <= 4096.
> Writing range->base (8 bytes) fills 4088-4095, but writing range->page_count
> (4 bytes) would write to 4096-4099, overflowing the kzalloc-allocated
> PAGE_SIZE buffer.

Fix this by accounting for the entry about to be written to, in addition to
the entries that are already allocated.

Fixes: 1ca5614b84ee ("crypto: ccp: Add support to initialize the AMD-SP for SEV-SNP")
Reported-by: Sashiko
Assisted-by: Gemini:gemini-3.1-pro-preview
Link: https://sashiko.dev/#/patchset/20260324161301.1353976-1-tycho%40kernel.org
Signed-off-by: Tycho Andersen (AMD) <tycho@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>