proc: Fix W=1 build kernel-doc warning

Building the kernel with W=1 generates the following warning:

  fs/proc/fd.c:81: warning: This comment starts with '/**',
                   but isn't a kernel-doc comment.

Use a normal comment for the helper function proc_fdinfo_permission().
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Link: https://lore.kernel.org/r/20241018102705.92237-2-thorsten.blum@linux.devSigned-off-by: Christian Brauner <brauner@kernel.org>

fs/proc/fd.c

@@ -77,7 +77,7 @@ static int seq_fdinfo_open(struct inode *inode, struct file *file)
 	return single_open(file, seq_show, inode);
 }
 
-/**
+/*
  * Shared /proc/pid/fdinfo and /proc/pid/fdinfo/fd permission helper to ensure
  * that the current task has PTRACE_MODE_READ in addition to the normal
  * POSIX-like checks.