scsi-generic: fix buffer overflow on block limits inquiry

Using linux 6.x guest, at boot time, an inquiry on a scsi-generic
device makes qemu crash.  This is caused by a buffer overflow when
scsi-generic patches the block limits VPD page.

Do the operations on a temporary on-stack buffer that is guaranteed
to be large enough.

Reported-by: Théo Maillart <tmaillart@freebox.fr>
Analyzed-by: Théo Maillart <tmaillart@freebox.fr>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>