mount.nfs: Eliminate compiler warnings in utils/mount/mount.c

mount.nfs: Eliminate compiler warnings in utils/mount/mount.c

Clean up.

mount.c: In function parse_opt:
mount.c:354: warning: conversion to size_t from int may change the
    sign of the result
mount.c:354: warning: conversion to int from size_t may change the
    sign of the result
mount.c:359: warning: conversion to size_t from int may change the
    sign of the result
mount.c:359: warning: conversion to int from size_t may change the
    sign of the result
mount.c: In function parse_opts:
mount.c:374: warning: conversion to int from size_t may change the
    sign of the result
mount.c:377: warning: conversion to size_t from int may change the
    sign of the result

Character string lengths are usually size_t anyway.  We can easily
avoid the implicit type cast here.

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