mount.nfs: Eliminate compiler warnings in utils/mount/version.h

mount.nfs: Eliminate compiler warnings in utils/mount/version.h

Clean up.

In file included from mount.c:50:
version.h: In function linux_version_code:
version.h:48: warning: conversion to unsigned int from int may
    change the sign of the result
version.h:48: warning: conversion to unsigned int from int may
    change the sign of the result
version.h:48: warning: conversion to unsigned int from int may
    change the sign of the result

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>