fit-image.bbclass: correct compress algorithm for kernel image

Change default `linux_comp` from `none` to `${FIT_KERNEL_COMP_ALG}`

Fixes: 650d9dc
("meta-phosphor: fit-image.bbclass: support compress kernel image")

Signed-off-by: James Chiang <cpchiang1@nuvoton.com>
Signed-off-by: Tim Lee <timlee660101@gmail.com>
Change-Id: Ib4baba203219ead75f7f3f0d1b082301f2e01ac1
diff --git a/meta-phosphor/classes/fit-image.bbclass b/meta-phosphor/classes/fit-image.bbclass
index f37aa02..bf0fc4f 100644
--- a/meta-phosphor/classes/fit-image.bbclass
+++ b/meta-phosphor/classes/fit-image.bbclass
@@ -12,7 +12,7 @@
 do_image_cpio[depends] += "virtual/kernel:do_deploy"
 
 run_assemble_fitimage() {
-    export linux_comp="none"
+    export linux_comp="${FIT_KERNEL_COMP_ALG}"
     fitimage_assemble $1.its $1.fitImage 1
 
     # The fitimage_assemble puts the image into DEPLOY_DIR_NAME due to