cmd: xtrace: Convert to bool

This variable is a boolean, not a string.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/configs/bcm_ns3_defconfig b/configs/bcm_ns3_defconfig
index d060097..5fb82e9 100644
--- a/configs/bcm_ns3_defconfig
+++ b/configs/bcm_ns3_defconfig
@@ -19,7 +19,7 @@
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="u-boot> "
-CONFIG_SYS_XTRACE="n"
+CONFIG_SYS_XTRACE=n
 CONFIG_CMD_GPT=y
 CONFIG_CMD_GPT_RENAME=y
 CONFIG_CMD_MMC=y