lib/mpi: return error code on dividing by zero

Definitely better to return error code than to divide by zero.
Signed-off-by: NDmitry Kasatkin <dmitry.kasatkin@intel.com>
Reviewed-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: NJames Morris <jmorris@namei.org>

lib/mpi/mpi-pow.c

@@ -59,7 +59,7 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
 	ep = exp->d;
 
 	if (!msize)
-		msize = 1 / msize;	/* provoke a signal */
+		return -EINVAL;
 
 	if (!esize) {
 		/* Exponent is zero, result is 1 mod MOD, i.e., 1 or 0