build: Fix typo in Armclang toolchain file

This caused a configuration time error for Corstone-315.

Change-Id: I3f3e29c26bfecbb6fbf2995f5d2d3911665e726b
Signed-off-by: Bence Balogh <bence.balogh@arm.com>
diff --git a/toolchain_ARMCLANG.cmake b/toolchain_ARMCLANG.cmake
index 94c360c..2a05f2d 100644
--- a/toolchain_ARMCLANG.cmake
+++ b/toolchain_ARMCLANG.cmake
@@ -361,7 +361,7 @@
         message(FATAL_ERROR "${target} is not an executable. Symbols cannot be shared from libraries.")
     endif()
 
-    foreach(symbol_list ${ARGN})
+    foreach(symbol_file ${ARGN})
         FILE(STRINGS ${symbol_file} SYMBOLS
             LENGTH_MINIMUM 1
         )