IB/cma: Make the code easier to verify

IB/cma: Make the code easier to verify

Static source code analysis tools like smatch cannot handle functions
that lock or not lock a mutex depending on the value of the arguments.
Hence inline the function cma_disable_callback(). Additionally, this
patch realizes a small performance optimization by reducing the number of
mutex_lock() and mutex_unlock() calls in the modified functions. With
this patch applied smatch no longer complains about source file cma.c.
Without this patch smatch reports the following for this source file:

drivers/infiniband/core/cma.c:1959: cma_req_handler() warn: inconsistent returns 'mutex:&listen_id->handler_mutex'.
  Locked on:   line 1880
               line 1959
  Unlocked on: line 1941
drivers/infiniband/core/cma.c:2112: iw_conn_req_handler() warn: inconsistent returns 'mutex:&listen_id->handler_mutex'.
  Locked on:   line 2048
  Unlocked on: line 2112

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Sean Hefty <sean.hefty@intel.com>
Cc: Steve Wise <swise@opengridcomputing.com>
Cc: Leon Romanovsky <leonro@mellanox.com>
Acked-by: Sean Hefty <sean.hefty@intel.com>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>