signal: improve comments

Improve the comments for pidfd_send_signal().
First, the comment still referred to a file descriptor for a process as a
"task file descriptor" which stems from way back at the beginning of the
discussion. Replace this with "pidfd" for consistency.
Second, the wording for the explanation of the arguments to the syscall
was a bit inconsistent, e.g. some used the past tense some used present
tense. Make the wording more consistent.
Signed-off-by: Christian Brauner <christian@brauner.io>

kernel/signal.c

@@ -3621,12 +3621,11 @@ static struct pid *pidfd_to_pid(const struct file *file)
 }
 
 /**
- * sys_pidfd_send_signal - send a signal to a process through a task file
- *                          descriptor
- * @pidfd:  the file descriptor of the process
- * @sig:    signal to be sent
- * @info:   the signal info
- * @flags:  future flags to be passed
+ * sys_pidfd_send_signal - Signal a process through a pidfd
+ * @pidfd:  file descriptor of the process
+ * @sig:    signal to send
+ * @info:   signal info
+ * @flags:  future flags
  *
  * The syscall currently only signals via PIDTYPE_PID which covers
  * kill(<positive-pid>, <signal>. It does not signal threads or process