system/physmem: Where we assume we have a RAM MR, assert it

system/physmem: Where we assume we have a RAM MR, assert it

In the functions invalidate_and_set_dirty() and
cpu_physical_memory_snapshot_and_clear_dirty(), we assume that we
are dealing with RAM memory regions. In this case we know that
memory_region_get_ram_addr() will succeed. Assert this before we
use the returned ram_addr_t in arithmetic.

This makes Coverity happier about these functions: it otherwise
complains that we might have an arithmetic overflow that stems
from the possible -1 return from memory_region_get_ram_addr().

Resolves: Coverity CID 1547629, 1547715

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-id: 20240723170513.1676453-1-peter.maydell@linaro.org