In the function weston_compositor_add_log_scope() we have
a struct weston_log_context parameter that in the .c file
is named log_ctx. In the .h, the same parameter is named
compositor. This is confusing, since its type is not
struct weston_compositor, but struct weston_log_context.
Rename the parameter in the .h to log_ctx.
Signed-off-by: Leandro Ribeiro <leandrohr@riseup.net>