i2c: at91: Initialize dma_buf in at91_twi_xfer()

stable inclusion
from stable-v5.10.121
commit f57696bc63418642f0f262ad8baded7d1192296f
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5L6CQ

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f57696bc63418642f0f262ad8baded7d1192296f

--------------------------------

[ Upstream commit 6977262c ]

Clang warns:

  drivers/i2c/busses/i2c-at91-master.c:707:6: warning: variable 'dma_buf' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
          if (dev->use_dma) {
              ^~~~~~~~~~~~
  drivers/i2c/busses/i2c-at91-master.c:717:27: note: uninitialized use occurs here
          i2c_put_dma_safe_msg_buf(dma_buf, m_start, !ret);
                                   ^~~~~~~

Initialize dma_buf to NULL, as i2c_put_dma_safe_msg_buf() is a no-op
when the first argument is NULL, which will work for the !dev->use_dma
case.

Fixes: 03fbb903 ("i2c: at91: use dma safe buffers")
Link: https://github.com/ClangBuiltLinux/linux/issues/1629Signed-off-by: NNathan Chancellor <nathan@kernel.org>
Reviewed-by: NMichael Walle <michael@walle.cc>
Signed-off-by: NWolfram Sang <wsa@kernel.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

drivers/i2c/busses/i2c-at91-master.c

@@ -657,7 +657,7 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
 	unsigned int_addr_flag = 0;
 	struct i2c_msg *m_start = msg;
 	bool is_read;
-	u8 *dma_buf;
+	u8 *dma_buf = NULL;
 
 	dev_dbg(&adap->dev, "at91_xfer: processing %d messages:\n", num);