mlx4_core: Use enum value GO_BIT_TIMEOUT_MSECS

Rename GO_BIT_TIMEOUT to GO_BIT_TIMEOUT_MSECS for clarity, and
actually use it as the go bit timeout (instead of having the define
but then ignoring it and using a hard-coded 10 * HZ for the actual
timeout).

Signed-off-by: Dotan Barak <dotanb@dev.mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>