NTB: remove handling of peer_sta from amd_link_is_up

amd_link_is_up() is a callback to inquire whether
the NTB link is up or not. So it should not indulge
itself into clearing the bitmasks of peer_sta.

Signed-off-by: Arindam Nath <arindam.nath@amd.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>