Change struct element order

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/bignum_mod.h b/library/bignum_mod.h
index ce871a9..2fb520c 100644
--- a/library/bignum_mod.h
+++ b/library/bignum_mod.h
@@ -45,8 +45,8 @@
 
 typedef struct
 {
-    size_t n;
     mbedtls_mpi_uint *p;
+    size_t n;
 } mbedtls_mpi_mod_residue;
 
 typedef void *mbedtls_mpi_mont_struct;