change format_get_indent() to use u32 instead of uword

This follows commit d3c008d108aa2187d1a2afe2833b4de25ca2c2ab by
Christophe Fontaine.

Change-Id: I0c4df40df44be2ac0ab25817fa050a1f619eca4d
Signed-off-by: Gabriel Ganne <gabriel.ganne@enea.com>
diff --git a/src/vppinfra/mheap.c b/src/vppinfra/mheap.c
index 47b7080..c703545 100644
--- a/src/vppinfra/mheap.c
+++ b/src/vppinfra/mheap.c
@@ -1165,7 +1165,8 @@
   int verbose = va_arg (*va, int);
 
   mheap_t *h;
-  uword i, size, indent;
+  uword i, size;
+  u32 indent;
   clib_mem_usage_t usage;
   mheap_elt_t *first_corrupt;