mei: vsc: Fix fortify-panic caused by invalid counted_by() use

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

mei: vsc: Fix fortify-panic caused by invalid counted_by() use

gcc 15 honors the __counted_by(len) attribute on vsc_tp_packet.buf[]

and the vsc-tp.c code is using this in a wrong way. len does not contain

the available size in the buffer, it contains the actual packet length

*without* the crc. So as soon as vsc_tp_xfer() tries to add the crc to

buf[] the fortify-panic handler gets triggered:

[ 80.842193] memcpy: detected buffer overflow: 4 byte write of buffer size 0

[ 80.842243] WARNING: CPU: 4 PID: 272 at lib/string_helpers.c:1032 __fortify_report+0x45/0x50

...

[ 80.843175] __fortify_panic+0x9/0xb

[ 80.843186] vsc_tp_xfer.cold+0x67/0x67 [mei_vsc_hw]

[ 80.843210] ? seqcount_lockdep_reader_access.constprop.0+0x82/0x90

[ 80.843229] ? lockdep_hardirqs_on+0x7c/0x110

[ 80.843250] mei_vsc_hw_start+0x98/0x120 [mei_vsc]

[ 80.843270] mei_reset+0x11d/0x420 [mei]

The easiest fix would be to just drop the counted-by but with the exception

of the ack buffer in vsc_tp_xfer_helper() which only contains enough room

for the packet-header, all other uses of vsc_tp_packet always use a buffer

of VSC_TP_MAX_XFER_SIZE bytes for the packet.

Instead of just dropping the counted-by, split the vsc_tp_packet struct

definition into a header and a full-packet definition and use a fixed

size buf[] in the packet definition, this way fortify-source buffer

overrun checking still works when enabled.