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

Commit b18aad71 ("IB/mthca: Fix RESET to ERROR transition") 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>