lib/mpi: mpi_read_raw_data(): purge redundant clearing of nbits

In mpi_read_raw_data(), unsigned nbits is calculated as follows:

 nbits = nbytes * 8;

and redundantly cleared later on if nbytes == 0:

  if (nbytes > 0)
    ...
  else
    nbits = 0;

Purge this redundant clearing for the sake of clarity.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>