x86: boot: fix unreachable else branch in boot_prep_linux

The else if branch uses the is_zimage boolean which is initialized to 0
and never set before being tested here.

remove the test on is_zimage to make this code reachable.

Signed-off-by: Guillaume Ranquet <ranquet.guillaume@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/x86/lib/bootm.c

@@ -103,7 +103,7 @@ static int boot_prep_linux(struct bootm_headers *images)
 		}
 		is_zimage = 1;
 #if defined(CONFIG_FIT)
-	} else if (images->fit_uname_os && is_zimage) {
+	} else if (images->fit_uname_os) {
 		ret = fit_image_get_data(images->fit_hdr_os,
 					 images->fit_noffset_os,
 					 (const void **)&data, &len);