Red Hat: CVE-2023-53553: kernel: HID: hyperv: avoid struct memcpy overrun warning (Multiple Advisories)

In the Linux kernel, the following vulnerability has been resolved:

HID: hyperv: avoid struct memcpy overrun warning

A previous patch addressed the fortified memcpy warning for most
builds, but I still see this one with gcc-9:

In file included from include/linux/string.h:254,
from drivers/hid/hid-hyperv.c:8:
In function 'fortify_memcpy_chk',
inlined from 'mousevsc_on_receive' at drivers/hid/hid-hyperv.c:272:3:
include/linux/fortify-string.h:583:4: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
583 | __write_overflow_field(p_size_field, size);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

My guess is that the WARN_ON() itself is what confuses gcc, so it no
longer sees that there is a correct range check. Rework the code in a
way that helps readability and avoids the warning.