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/test/avb_util_unittest.cc b/test/avb_util_unittest.cc
index d0d6b87..dc0116f 100644
--- a/test/avb_util_unittest.cc
+++ b/test/avb_util_unittest.cc
@@ -282,7 +282,7 @@
   nbf = 36 + sizeof(AvbChainPartitionDescriptor) - sizeof(AvbDescriptor);
   h.parent_descriptor.num_bytes_following = htobe64(nbf);
   h.parent_descriptor.tag = htobe64(AVB_DESCRIPTOR_TAG_CHAIN_PARTITION);
-  h.rollback_index_slot = htobe32(42);
+  h.rollback_index_location = htobe32(42);
   h.partition_name_len = htobe32(16);
   h.public_key_len = htobe32(17);
 
@@ -290,7 +290,7 @@
 
   EXPECT_EQ(AVB_DESCRIPTOR_TAG_CHAIN_PARTITION, s.parent_descriptor.tag);
   EXPECT_EQ(nbf, s.parent_descriptor.num_bytes_following);
-  EXPECT_EQ(42UL, s.rollback_index_slot);
+  EXPECT_EQ(42UL, s.rollback_index_location);
   EXPECT_EQ(16UL, s.partition_name_len);
   EXPECT_EQ(17UL, s.public_key_len);
 
@@ -301,7 +301,7 @@
 
   // Check for bad rollback index slot (must be at least 1).
   bad = h;
-  bad.rollback_index_slot = htobe32(0);
+  bad.rollback_index_location = htobe32(0);
   EXPECT_EQ(0, avb_chain_partition_descriptor_validate_and_byteswap(&bad, &s));
 
   // Doesn't fit in 40 bytes (24 + 17 = 41).