Some older versions of gcc (observed with gcc 4.7.2) report a spurious
uninitialised variable warning in ena_get_device_attributes().  Work
around this warning by manually inlining the relevant code (which has
only a single call site).

Reported-by: xbgmsharp <xbgmsharp@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

Signed-off-by: Michael Brown <mcb30@ipxe.org>