[GitHub Actions] Disable sparse declaration-after-statement

"error: mixing declarations and code" floods in
./include/linux/page-flags.h which is included in some sound drivers.

Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>

Author: bardliao

.github/workflows/buildtest.yml

@@ -30,7 +30,7 @@ jobs:
 
       - name: build start
         run: |
-          export ARCH=x86_64 CF="-Wsparse-error -Wsparse-all -Wno-bitwise-pointer -Wno-pointer-arith -Wno-typesign -Wnoshadow -Wnoflexible-array-array -Wnoflexible-array-nested -Wnoflexible-array-sizeof -Wnoflexible-array-union -Wnotautological-compare -Wno-transparent-union -Wno-constexpr-not-const"
+          export ARCH=x86_64 CF="-Wsparse-error -Wsparse-all -Wno-bitwise-pointer -Wno-pointer-arith -Wno-typesign -Wnoshadow -Wnoflexible-array-array -Wnoflexible-array-nested -Wnoflexible-array-sizeof -Wnoflexible-array-union -Wnotautological-compare -Wno-transparent-union -Wno-constexpr-not-const -Wno-declaration-after-statement"
           make allmodconfig
           make modules_prepare
           make -k sound/soc/sof/ C=2