HAL_ChibiOS: use calloc for malloc type

this is not strictly necessary on ChibiOS as we already override
malloc, but will keep static analysis happy

libraries/AP_HAL_ChibiOS/Util.cpp

@@ -52,7 +52,7 @@ void* Util::malloc_type(size_t size, AP_HAL::Util::Memory_Type mem_type)
     if (mem_type == AP_HAL::Util::MEM_FAST) {
         return try_alloc_from_ccm_ram(size);
     } else {
-        return malloc(size);
+        return calloc(1, size);
     }
 }
 
@@ -69,7 +69,7 @@ void* Util::try_alloc_from_ccm_ram(size_t size)
     void *ret = malloc_ccm(size);
     if (ret == nullptr) {
         //we failed to allocate from CCM so we are going to try common SRAM
-        ret = malloc(size);
+        ret = calloc(1, size);
     }
     return ret;
 }