twister: Remove testcase-root reference

--testcase-root got renamed to --testsuite-root

Signed-off-by: Reto Schneider <reto.schneider@husqvarnagroup.com>
diff --git a/scripts/pylib/twister/twisterlib.py b/scripts/pylib/twister/twisterlib.py
index 9171343..aeebffa 100755
--- a/scripts/pylib/twister/twisterlib.py
+++ b/scripts/pylib/twister/twisterlib.py
@@ -1749,7 +1749,7 @@
         a testcase.yaml can define multiple tests, the canonical name for
         the test case is <workdir>/<name>.
 
-        @param testsuite_root os.path.abspath() of one of the --testcase-root
+        @param testsuite_root os.path.abspath() of one of the --testsuite-root
         @param workdir Sub-directory of testsuite_root where the
             .yaml test configuration file was found
         @param name Name of this test case, corresponding to the entry name