tests: Kconfig: add proper description to config option

Add proper description to the TEST_EXTRA_STACKSIZE config
option prompt message.

Signed-off-by: Ramakrishna Pallala <ramakrishna.pallala@intel.com>
diff --git a/tests/Kconfig b/tests/Kconfig
index 7dbf0c3..2332da6 100644
--- a/tests/Kconfig
+++ b/tests/Kconfig
@@ -17,7 +17,7 @@
 	  test defaults.
 
 config TEST_EXTRA_STACKSIZE
-	int "Test function thread stack size"
+	int "Test function extra thread stack size"
 	default 0
 	default 768 if XTENSA
 	help