symbolize.py: add line removed by mistake

Commit c0c57c8fa583 ("symbolize.py: fix stack dump of TEE core with
pager") has mistakenly removed a line which caches the name of the ELF
file for which addr2line was last spawned. As a result, processes keep
being killed and re-started, resulting in a much slower execution.

This commit restores the missing line.

Fixes: c0c57c8fa583 ("symbolize.py: fix stack dump of TEE core with pager")
Signed-off-by: Jerome Forissier <jerome@forissier.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/scripts/symbolize.py b/scripts/symbolize.py
index 4f5e226..a622475 100755
--- a/scripts/symbolize.py
+++ b/scripts/symbolize.py
@@ -164,6 +164,7 @@
         if not cmd:
             return
         self._addr2line = self.my_Popen([cmd, '-f', '-p', '-e', elf])
+        self._addr2line_elf_name = elf_name
 
     # If addr falls into a region that maps a TA ELF file, return the load
     # address of that file.