smb.c: Fixed compilation warnings

smb.c:322: warning: conversion to 'short unsigned int' from 'unsigned
           int' may alter its value
smb.c:323: warning: conversion to 'short unsigned int' from 'unsigned
           int' may alter its value
smb.c:482: warning: conversion to 'short unsigned int' from 'int' may
           alter its value
smb.c:521: warning: conversion to 'unsigned int' from 'curl_off_t' may
           alter its value
smb.c:549: warning: conversion to 'unsigned int' from 'curl_off_t' may
           alter its value
smb.c:550: warning: conversion to 'short unsigned int' from 'int' may
           alter its value