common: cosmetic: CONFIG_BOOTFILE checkpatch compliance

Remove MK_STR from places that consume CONFIG_BOOTFILE to force all definitions to be string literals.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Cc: Joe Hershberger <joe.hershberger@gmail.com>
Cc: Wolfgang Denk <wd@denx.de>
Acked-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/include/configs/mpr2.h b/include/configs/mpr2.h
index f32899f..0f7edff 100644
--- a/include/configs/mpr2.h
+++ b/include/configs/mpr2.h
@@ -35,7 +35,7 @@
 /* Default environment variables */
 #define CONFIG_BAUDRATE		115200
 #define CONFIG_BOOTARGS		"console=ttySC0,115200"
-#define CONFIG_BOOTFILE		/boot/zImage
+#define CONFIG_BOOTFILE		"/boot/zImage"
 #define CONFIG_LOADADDR		0x8E000000
 #define CONFIG_VERSION_VARIABLE