dev-amdgpu: Hotfix variable initialization

These non-initialized variables were causing the trace reader not to
record all lines.

Change-Id: I88764493d8124c072bc90ff9c08aa26421467f7b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/53063
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/src/dev/amdgpu/mmio_reader.hh b/src/dev/amdgpu/mmio_reader.hh
index 6c88f0b..a057183 100644
--- a/src/dev/amdgpu/mmio_reader.hh
+++ b/src/dev/amdgpu/mmio_reader.hh
@@ -99,9 +99,9 @@
     trace_BAR_t trace_BARs[6];
 
     /* Indexes used to print driver loading progress. */
-    uint64_t trace_index;
-    uint64_t trace_final_index;
-    uint64_t trace_cur_index;
+    uint64_t trace_index = 0;
+    uint64_t trace_final_index = 0;
+    uint64_t trace_cur_index = 0;
 
     /* An entry in the MMIO trace. */
     struct MmioTrace