Small issues in passing-data example

[ccorcoveanu]

I found some issues in the passing data example:
https://docs.wasmer.io/integrations/c/examples/passing-data

First, the path to the wasm module (example-wasienv-wasm/strings-wasm-is-cool/strings-wasm-is-cool.wasm) seems to a different one than the one pointed to use.

On the premise that the correct one is this: https://github.com/wasmerio/docs.wasmer.io/blob/master/integrations/shared/c/passing-data.c, there are some fixes to be made.

First, when calling the add_wasm_is_cool function, the length of the original string should be passed as an argument. The second one is that the function that returns the pointer to the byte_buffer is called get_wasm_memory_buffer_pointer instead of get_buffer_pointer