e1000: Fix msi enable leak on error, don't print error message, cleanup

pci_enable_msi failure is a normal event so we should not print any error.
Going over the code I spotted a missing pci_disable_msi() leak when irq
allocation fails. The whole code also needed a cleanup, so I combined the
two different calls to pci_request_irq into a single call making this
look a lot better. All #ifdef CONFIG_PCI_MSI's have been removed.

Compile tested with both CONFIG_PCI_MSI enabled and disabled.

Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>