PCI: mn10300: use generic pcibios_set_master()

This patch removes mn10300's architecture-specific 'pcibios_set_master()'
routine for ASB2305 and lets the default PCI core based implementation
handle PCI device 'latency timer' setup.

No functional change.

Signed-off-by: Myron Stowe <myron.stowe@redhat.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>