PCI MSI: shorten PCI_MSIX_ENTRY_* symbol names

These names are too long!  Drop _OFFSET to save some bytes/lines.

Reviewed-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>