kthread: fix spelling typo and grammar in comments

- `If present` -> `If present,'
- `reuturn` -> `return`
- `function exit safely` -> `function to exit safely`

Link: https://lkml.kernel.org/r/20230502090242.3037194-1-quic_pbaronia@quicinc.com
Signed-off-by: Prathu Baronia <quic_pbaronia@quicinc.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zqiang <qiang1.zhang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

kernel/kthread.c

@@ -312,10 +312,10 @@ void __noreturn kthread_exit(long result)
  * @comp: Completion to complete
  * @code: The integer value to return to kthread_stop().
  *
- * If present complete @comp and the reuturn code to kthread_stop().
+ * If present, complete @comp and then return code to kthread_stop().
  *
  * A kernel thread whose module may be removed after the completion of
- * @comp can use this function exit safely.
+ * @comp can use this function to exit safely.
  *
  * Does not return.
  */