log: correct CONFIG_LOG_TEST prerequisites

An error

	undefined reference to `do_log_test'

occurs for CONFIG_CMD_LOG=y, CONFIG_LOG_TEST=y, CONGIG_UNIT_TEST=n

Make CONFIG_UNIT_TEST a prerequisite.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/Kconfig b/common/Kconfig
index 3072651..40da8fa 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -777,7 +777,7 @@
 
 config LOG_TEST
 	bool "Provide a test for logging"
-	depends on LOG
+	depends on LOG && UNIT_TEST
 	default y if SANDBOX
 	help
 	  This enables a 'log test' command to test logging. It is normally