arm: armv7-a: Fix kernel stack dump in arm_assert.c

Summary:
- This commit fixes kernel stack dump information

Impact:
- Affects armv7-a with kernel build

Testing:
- Built with sama5d4-ek:knsh
- Not tested

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

arch/arm/src/armv7-a/arm_assert.c

@@ -252,7 +252,7 @@ static void up_dumpstate(void)
   if (rtcb->xcp.kstack)
     {
       kstackbase = (uint32_t)rtcb->xcp.kstack +
-                   CONFIG_ARCH_KERNEL_STACKSIZE - 4;
+                   CONFIG_ARCH_KERNEL_STACKSIZE;
 
       _alert("Kernel stack:\n");
       _alert("  base: %08x\n", kstackbase);