printk: Remove obsoleted check for non-existent "user" object

The original check for non-null "user" object was introduced by commit
e11fea9 ("kmsg: export printk records to the /dev/kmsg interface")
when "user" could be NULL if /dev/ksmg was opened for writing.

Subsequent change 750afe7 ("printk: add kernel parameter to control
writes to /dev/kmsg") made "user" context required for files opened for
write, but didn't remove now redundant checks for it to be non-NULL.

This patch removes the dead code while preserving the current logic.

Signed-off-by: Stanislav Kinsburskii <stanislav.kinsburski@gmail.com>
CC: Petr Mladek <pmladek@suse.com>
CC: Sergey Senozhatsky <senozhatsky@chromium.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: John Ogness <john.ogness@linutronix.de>
CC: linux-kernel@vger.kernel.org
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/167929571877.2810.9926967619100618792.stgit@skinsburskii.localdomain

Author: Stanislav Kinsburskii

kernel/printk/printk.c

@@ -730,7 +730,7 @@ static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
 	size_t len = iov_iter_count(from);
 	ssize_t ret = len;
 
-	if (!user || len > PRINTKRB_RECORD_MAX)
+	if (len > PRINTKRB_RECORD_MAX)
 		return -EINVAL;
 
 	/* Ignore when user logging is disabled. */
@@ -792,9 +792,6 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 	};
 	ssize_t ret;
 
-	if (!user)
-		return -EBADF;
-
 	ret = mutex_lock_interruptible(&user->lock);
 	if (ret)
 		return ret;
@@ -859,8 +856,6 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 	struct devkmsg_user *user = file->private_data;
 	loff_t ret = 0;
 
-	if (!user)
-		return -EBADF;
 	if (offset)
 		return -ESPIPE;
 
@@ -893,9 +888,6 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 	struct printk_info info;
 	__poll_t ret = 0;
 
-	if (!user)
-		return EPOLLERR|EPOLLNVAL;
-
 	poll_wait(file, &log_wait, wait);
 
 	if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
@@ -944,9 +936,6 @@ static int devkmsg_release(struct inode *inode, struct file *file)
 {
 	struct devkmsg_user *user = file->private_data;
 
-	if (!user)
-		return 0;
-
 	ratelimit_state_exit(&user->rs);
 
 	mutex_destroy(&user->lock);