arm64/sme: Fix NULL check after kzalloc

Fix following coccicheck error:
./arch/arm64/kernel/process.c:322:2-23: alloc with no test, possible model on line 326

Here should be dst->thread.sve_state.

Fixes: 8bd7f91 ("arm64/sme: Implement traps and syscall handling for SME")
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Reviwed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220426113054.630983-1-wanjiabing@vivo.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: Wan Jiabing

arch/arm64/kernel/process.c

@@ -321,7 +321,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 	if (thread_za_enabled(&src->thread)) {
 		dst->thread.sve_state = kzalloc(sve_state_size(src),
 						GFP_KERNEL);
-		if (!dst->thread.za_state)
+		if (!dst->thread.sve_state)
 			return -ENOMEM;
 		dst->thread.za_state = kmemdup(src->thread.za_state,
 					       za_state_size(src),