smb.c: Fixed compilation warnings

smb.c:780: warning: passing 'char *' to parameter of type 'unsigned
           char *' converts between pointers to integer types with
           different sign
smb.c:781: warning: passing 'char *' to parameter of type 'unsigned
           char *' converts between pointers to integer types with
           different sign
smb.c:804: warning: passing 'char *' to parameter of type 'unsigned
           char *' converts between pointers to integer types with
           different sign