smbios: Fix assertion on socket count calculation

QEMU currently allows the number of VCPUs to not be a multiple of the
number of threads per socket, but the smbios socket count calculation
introduced by commit c97294ec doesn't
take that into account, triggering an assertion. e.g.:

  $ ./x86_64-softmmu/qemu-system-x86_64 -smp 4,sockets=2,cores=6,threads=1
  qemu-system-x86_64: /home/ehabkost/rh/proj/virt/qemu/hw/i386/smbios.c:825: smbios_get_tables: Assertion `smbios_smp_sockets >= 1' failed.
  Aborted (core dumped)

Socket count calculation doesn't belong to smbios.c and should
eventually be moved to the main SMP topology configuration code. But
while we don't move the code, at least make it correct by rounding up
the division.

Cc: Gabriel Somlo <somlo@cmu.edu>
Cc: qemu-stable@nongnu.org
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-By: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>