net: dsa: mv88e6xxx: use BMSR_ANEGCOMPLETE bit for filling an_complete

Commit ede359d8 ("net: dsa: mv88e6xxx: Link in pcs_get_state() if AN
is bypassed") added the ability to link if AN was bypassed, and added
filling of state->an_complete field, but set it to true if AN was
enabled in BMCR, not when AN was reported complete in BMSR.

This was done because for some reason, when I wanted to use BMSR value
to infer an_complete, I was looking at BMSR_ANEGCAPABLE bit (which was
always 1), instead of BMSR_ANEGCOMPLETE bit.

Use BMSR_ANEGCOMPLETE for filling state->an_complete.

Fixes: ede359d8 ("net: dsa: mv88e6xxx: Link in pcs_get_state() if AN is bypassed")
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>