Makefile: use two double-quotations as a pair

Some editors such as Emacs can highlight source files.
But their parser algorithm is not perfect.

If you use one double-quotation alone, some editor cannot
handle it nicely and mark source lines as a string by mistake.

It is preferable to use two double-quotations as a pair.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/spl/Makefile b/spl/Makefile
index 2a787af..b816e20 100644
--- a/spl/Makefile
+++ b/spl/Makefile
@@ -37,7 +37,7 @@
 HAVE_VENDOR_COMMON_LIB = $(if $(wildcard $(SRCTREE)/board/$(VENDOR)/common/Makefile),y,n)
 
 ifdef	CONFIG_SPL_START_S_PATH
-START_PATH := $(subst ",,$(CONFIG_SPL_START_S_PATH))
+START_PATH := $(CONFIG_SPL_START_S_PATH:"%"=%)
 else
 START_PATH := $(CPUDIR)
 endif
@@ -118,7 +118,7 @@
 # Linker Script
 ifdef CONFIG_SPL_LDSCRIPT
 # need to strip off double quotes
-LDSCRIPT := $(addprefix $(SRCTREE)/,$(subst ",,$(CONFIG_SPL_LDSCRIPT)))
+LDSCRIPT := $(addprefix $(SRCTREE)/,$(CONFIG_SPL_LDSCRIPT:"%"=%))
 endif
 
 ifeq ($(wildcard $(LDSCRIPT)),)