core-image-kernel-dev.bb: Standardize use of _append and leading space.

(From OE-Core rev: 00027aee12f4bbc9a4ba607c91fcc1e0e8257fa2)

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-extended/images/core-image-kernel-dev.bb

@@ -14,7 +14,7 @@ CORE_IMAGE_EXTRA_INSTALL += "${KERNEL_DEV_MODULE} \
                             "
 
 # We need extra space for things like kernel builds, etc.
-IMAGE_ROOTFS_EXTRA_SPACE_append += "+ 3000000"
+IMAGE_ROOTFS_EXTRA_SPACE_append = " + 3000000"
 
 # Let's define our own subset to test, we can later add a on-target kernel build even!
 DEFAULT_TEST_SUITES = "ping ssh df connman syslog scp date parselogs"