scsi: target: file: Use kzalloc_flex for aio_cmd

The target_core_file doesn't initialize the aio_cmd->iocb for the
ki_write_stream. When a write command fd_execute_rw_aio() is executed,
we may get a bogus ki_write_stream value, causing unintended write
failure status when checking iocb->ki_write_stream > max_write_streams
in the block device.

Let's just use kzalloc_flex when allocating the aio_cmd and let
ki_write_stream=0 to fix this issue.

Fixes: 732f25a2895a ("fs: add a write stream field to the kiocb")
Fixes: c27683da6406 ("block: expose write streams for block device nodes")
Cc: [e-mail]
Signed-off-by: Thinh Nguyen <[e-mail]>
Link: https://patch.msgid.link/f1a2[e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/target/target_core_file.c

···
 	ssize_t len = 0;
 	int ret = 0, i;
 
-	aio_cmd = kmalloc_flex(*aio_cmd, bvecs, sgl_nents);
+	aio_cmd = kzalloc_flex(*aio_cmd, bvecs, sgl_nents);
 	if (!aio_cmd)
 		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;