fs/pipe.c: local vars have to match types of proper pipe_inode_info fields

fs/pipe.c: local vars have to match types of proper pipe_inode_info fields

head, tail, ring_size are declared as unsigned int, so all local variables
that operate with these fields have to be unsigned to avoid signed integer
overflow.

Right now, it isn't an issue because the maximum pipe size is limited by
1U<<31.

Link: https://lkml.kernel.org/r/20220106171946.36128-1-avagin@gmail.com
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Suggested-by: Dmitry Safonov <0x7f454c46@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>