CMake: PA_ALSA_DYNAMIC defaults to OFF, docs says defaults to ON

[RossBencina]

CMakeLists.txt line 353:

option(PA_ALSA_DYNAMIC "Enable dynamically loading libasound with dlopen using PaAlsa_SetLibraryPathName" OFF)

compile_cmake.dox lines 278-281:

@note All options here default to `ON` if available except for the OSS, ASIO, and skeleton backends.

- **`-DPA_USE_ALSA=ON|OFF`**: (Linux/Unix-like/etc. Only). Use the ASLA host API. Requires ALSA.
    - **`-DPA_ALSA_DYNAMIC=ON|OFF`**: Dynamically load libasound with dlopen using @ref PaAlsa_SetLibraryPathName.

Probably be better to tell the user how to run CMake to get the default values rather than making promises in the docs.