spl: fix descending condition to drivers/mtd/nand/

SPL should not reference CONFIG_CMD_NAND to decide whether or not
it should build drivers/mtd/nand.  CONFIG_CMD_NAND should be only
used to select the NAND utility command on the command parser.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/scripts/Makefile.spl b/scripts/Makefile.spl
index 69f7c9f..342d82e 100644
--- a/scripts/Makefile.spl
+++ b/scripts/Makefile.spl
@@ -77,7 +77,7 @@
 libs-$(CONFIG_SPL_LIBGENERIC_SUPPORT) += lib/
 libs-$(CONFIG_SPL_POWER_SUPPORT) += drivers/power/ drivers/power/pmic/
 libs-$(CONFIG_SPL_MTD_SUPPORT) += drivers/mtd/
-libs-$(if $(CONFIG_CMD_NAND),$(CONFIG_SPL_NAND_SUPPORT)) += drivers/mtd/nand/
+libs-$(CONFIG_SPL_NAND_SUPPORT) += drivers/mtd/nand/
 libs-$(CONFIG_SPL_DRIVERS_MISC_SUPPORT) += drivers/misc/
 libs-$(CONFIG_SPL_ONENAND_SUPPORT) += drivers/mtd/onenand/
 libs-$(CONFIG_SPL_DMA_SUPPORT) += drivers/dma/