Char: stallion, fix compiler warnings

Don't emit warnings on 64 bit platforms from min(). sizeof() on those
is not uint, neither 2 pointers difference, cast it to uint by min_t in
both cases.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>