mx_size_t -> size_t

Change-Id: I184bcf3119a5944df7a17e7c1eccc55103421a79
diff --git a/src/utils/os_fuchsia.c b/src/utils/os_fuchsia.c
index fc73e14..4dfc8d6 100644
--- a/src/utils/os_fuchsia.c
+++ b/src/utils/os_fuchsia.c
@@ -153,11 +153,11 @@
   if (TEST_FAIL()) return -1;
 
   while (len > 0) {
-    mx_size_t output_bytes_this_pass = MX_CPRNG_DRAW_MAX_LEN;
+    size_t output_bytes_this_pass = MX_CPRNG_DRAW_MAX_LEN;
     if (len < (size_t)output_bytes_this_pass) {
       output_bytes_this_pass = len;
     }
-    mx_size_t bytes_drawn;
+    size_t bytes_drawn;
     mx_status_t status = mx_cprng_draw(buf, output_bytes_this_pass, &bytes_drawn);
     if (status != NO_ERROR) {
       abort();