refactor(mm): minor refactors to `mm.c`

* rename parameters for consistency
* mark parameters const where possible
* reduce scope of loop variables

Change-Id: I920a6fea17d4dcc36281918cba46884d353fdfd8
Signed-off-by: Karl Meakin <karl.meakin@arm.com>
diff --git a/src/mm_test.cc b/src/mm_test.cc
index 9a49c21..34c72a4 100644
--- a/src/mm_test.cc
+++ b/src/mm_test.cc
@@ -52,10 +52,10 @@
 /**
  * Checks whether the address is mapped in the address space.
  */
-bool mm_vm_is_mapped(struct mm_ptable *t, ipaddr_t ipa)
+bool mm_vm_is_mapped(struct mm_ptable *ptable, ipaddr_t ipa)
 {
 	uint32_t mode;
-	return mm_vm_get_mode(t, ipa, ipa_add(ipa, 1), &mode) &&
+	return mm_vm_get_mode(ptable, ipa, ipa_add(ipa, 1), &mode) &&
 	       (mode & MM_MODE_INVALID) == 0;
 }