Silence Clang -Wpointer-sign warning.

Clang displays warnings like the following one while compiling binary.c.

    binary.c:449:16: warning: passing 'u_char *' (aka 'unsigned char *') to parameter of
    type 'char *' converts between pointers to integer types with different sign [-Wpointer-sign]
    inject(uv, &v, off, 1);