CMakeLists: Use correct name for Tremor library.

Fixes #702.

(cherry picked from commit 51b73d0)

Author: icculus

CMakeLists.txt

@@ -529,7 +529,7 @@ if(SDLMIXER_VORBIS_TREMOR)
         find_package(tremor ${required})
         if(tremor_FOUND)
             if(NOT SDLMIXER_VORBIS_TREMOR_SHARED)
-                list(APPEND PC_REQUIRES tremor)
+                list(APPEND PC_REQUIRES vorbisidec)
             endif()
             set(SDLMIXER_VORBIS_TREMOR_ENABLED TRUE)
         else()