Rename "rollback index slot" to "rollback index location".

This is because the word slot is already used in the context of
A/B. Less confusing this way.

Bug: 33100927
Test: New unit tests and all unit tests pass.
Test: Manually tested on UEFI based bootloader.

Change-Id: Ic611b02dc18e7dd9f14c2c87b247be3cd8f4aaf2
diff --git a/libavb_ab/avb_ab_flow.c b/libavb_ab/avb_ab_flow.c
index 6b67c6a..37f0216 100644
--- a/libavb_ab/avb_ab_flow.c
+++ b/libavb_ab/avb_ab_flow.c
@@ -291,9 +291,9 @@
 
   /* Update stored rollback index such that the stored rollback index
    * is the largest value supporting all currently bootable slots. Do
-   * this for every rollback index slot.
+   * this for every rollback index location.
    */
-  for (n = 0; n < AVB_MAX_NUMBER_OF_ROLLBACK_INDEX_SLOTS; n++) {
+  for (n = 0; n < AVB_MAX_NUMBER_OF_ROLLBACK_INDEX_LOCATIONS; n++) {
     uint64_t rollback_index_value = 0;
 
     if (slot_data[0] != NULL && slot_data[1] != NULL) {