linux: use positive logic to define initramfs fixups

Commit d06dca38bb03 (linux: cleanup kconfig fixup processing) introduced
the conditional LINUX_KCONFIG_FIXUP_CMDS_ROOTFS_CPIO, using a negative
logic condition.

Switch that to use positive logic.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

linux/linux.mk

@@ -370,7 +370,7 @@ endif
 # built, we create a fake cpio file. It'll be
 # replaced later by the real cpio archive, and the kernel will be
 # rebuilt using the linux-rebuild-with-initramfs target.
-ifneq ($(BR2_TARGET_ROOTFS_INITRAMFS),)
+ifeq ($(BR2_TARGET_ROOTFS_INITRAMFS),y)
 define LINUX_KCONFIG_FIXUP_CMDS_ROOTFS_CPIO
 	@mkdir -p $(BINARIES_DIR)
 	$(Q)touch $(BINARIES_DIR)/rootfs.cpio