Revert "vmci: Prevent the dispatching of uninitialized payloads"

This reverts commit bfb4cf9fb97e4063f0aa62e9e398025fb6625031.

While the code "looks" correct, the compiler has no way to know that
doing "fun" pointer math like this really isn't a write off the end of
the structure as there is no hint anywhere that the structure has data
at the end of it.

This causes the following build warning:

In function 'fortify_memset_chk',
inlined from 'ctx_fire_notification.isra' at drivers/misc/vmw_vmci/vmci_context.c:254:3:
include/linux/fortify-string.h:480:25: 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]
480 | __write_overflow_field(p_size_field, size);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

So revert it for now and it can come back in the future in a "sane" way
that either correctly makes the structure know that there is trailing
data, OR just the payload structure is properly referenced and zeroed
out.

Fixes: bfb4cf9fb97e ("vmci: Prevent the dispatching of uninitialized payloads")
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Lizhi Xu <lizhi.xu@windriver.com>
Link: https://lore.kernel.org/r/20250703171021.0aee1482@canb.auug.org.au
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>