IB/mlx4: Remove extra code for RESET->ERR QP state transition

Commit 65adfa91 ("IB/mlx4: Fix RESET to RESET and RESET to ERROR
transitions") added some extra code to handle a QP state transition
from RESET to ERROR.  However, the latest 1.2.1 version of the IB spec
has clarified that this transition is actually not allowed, so we can
remove this extra code again.

Signed-off-by: Roland Dreier <rolandd@cisco.com>