PCI: consolidate duplicated MSI enable functions

Two recent patches added basically the same code to turn on
HT MSI mapping:

    http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=6bae1d96
    http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=9dc625e7



There's no need to have both, so this patch removes one copy.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>