Cleanup USB and partition defines

disk/part.c

diff --git a/disk/part.c b/disk/part.c
index 0e9ddbd..2255e72 100644
--- a/disk/part.c
+++ b/disk/part.c
@@ -36,7 +36,8 @@
 #if ((CONFIG_COMMANDS & CFG_CMD_IDE)	|| \
      (CONFIG_COMMANDS & CFG_CMD_SCSI)	|| \
      (CONFIG_COMMANDS & CFG_CMD_USB)	|| \
-     (CONFIG_MMC) || (CONFIG_SYSTEMACE) )
+     defined(CONFIG_MMC) || \
+     defined(CONFIG_SYSTEMACE) )
 
 /* ------------------------------------------------------------------------- */
 /*