IB/rdmavt: Correct sparse annotation

The __must_hold() is sufficent to correct the sparse
context imbalance inside a function.

Per Documentation/sparse.txt:
__must_hold - The specified lock is held on function entry and exit.

Fixes: Commit c0a67f6b ("IB/rdmavt: Annotate rvt_reset_qp()")
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>