lib/mpi: Add the return value check of kcalloc()

Add the return value check of kcalloc() to avoid potential
NULL ptr dereference.

Fixes: a8ea8bdd9d ("lib/mpi: Extend the MPI library")
Signed-off-by: Zizhuang Deng <sunsetdzz@gmail.com>
Reviewed-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

lib/mpi/mpi-mod.c

@@ -40,6 +40,8 @@ mpi_barrett_t mpi_barrett_init(MPI m, int copy)
 
 	mpi_normalize(m);
 	ctx = kcalloc(1, sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return NULL;
 
 	if (copy) {
 		ctx->m = mpi_copy(m);