glib: Fix some misuses of gsize/size_t types

glib: Fix some misuses of gsize/size_t types

This unbreaks cross compile builds:

configure --target-list="i386-softmmu" --cpu=i386

When building on a 64bit machine.

Reported-by: David Holsgrove <david.holsgrove@xilinx.com>
Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
Message-id: 926326e96fd8685d74e9d5bf430fe4ad97a55289.1369191585.git.peter.crosthwaite@xilinx.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>