e1000: Made an adapter struct variable into a local (txb2b)

Made an adapter struct variable into a local (txb2b)


Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: John Ronciak <john.ronciak@intel.com>