e1000: clean LTO warnings

During LTO build compiler reports some 'false positive' warnings about
variables being possibly used uninitialized. This patch silences these
warnings.

Exemplary compiler warning to suppress (with LTO enabled):
error: 'link' may be used uninitialized in this function
[-Werror=maybe-uninitialized]

if (link) {

Signed-off-by: Andrzej Ostruszka <aostruszka@marvell.com>

Approved by: imp
Obtained from: DPDK (46136031f19107f4e9b6b3a952cb7f57877a7f0f)
MFC after: 1 week

(cherry picked from commit 089cdb3990f47be3cd34d1a57567a2e89c917929)