SDL_mixer: build: Fix detection of libvorbisfile

SDL Commits
1 
From 328c0d733d8481055831d0194c27ffb11dbffe86 Mon Sep 17 00:00:00 2001
From: Simon McVittie <[EMAIL REDACTED]>
Date: Tue, 19 Sep 2023 19:57:41 +0100
Subject: [PATCH] build: Fix detection of libvorbisfile

The variable name is case-sensitive and the module is named `Vorbis`,
not `vorbis`.

Signed-off-by: Simon McVittie <smcv@collabora.com>
---
 CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 18e54ac9..649f522f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -589,7 +589,7 @@ if(SDL3MIXER_VORBIS_VORBISFILE)
         endif()
     else()
         find_package(Vorbis ${required})
-        if(vorbis_FOUND)
+        if(Vorbis_FOUND)
             set(SDL3MIXER_VORBIS_VORBISFILE_ENABLED TRUE)
             message(STATUS "Using system vorbisfile")
             if(NOT SDL3MIXER_VORBIS_VORBISFILE_SHARED)