ibm_newemac: Fix typo in flow control config option

The recent build fix for ibm_newemac has a typo in the config
option #ifdef used for disabling flow control.  This corrects
it to the proper Kconfig option name.

Reported-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>