Fix the type of the callback in getprop.

Fixes:

  toys/android/getprop.c:56:39: warning: incompatible pointer types
    passing 'void (void *, const char *, const char *)' to parameter of
    type 'void (*)(void *, const char *, const char *, uint32_t)'
    (aka 'void (*)(void *, const char *, const char *, unsigned int)')
    [-Wincompatible-pointer-types]

  __system_property_read_callback(pi, read_callback, NULL);
                                      ^~~~~~~~~~~~~
1 file changed