tests/amdgpu: s/uvd_messages.h/decode_messages.h/ in Makefile.am

Fixes make distcheck with amdgpu enabled.

Fixes: ec65d1980912 ("tests/amdgpu: rename uvd messages to decode
                      messages")

Trivial.
diff --git a/tests/amdgpu/Makefile.am b/tests/amdgpu/Makefile.am
index d4572be..9e08578 100644
--- a/tests/amdgpu/Makefile.am
+++ b/tests/amdgpu/Makefile.am
@@ -23,7 +23,7 @@
 	basic_tests.c \
 	bo_tests.c \
 	cs_tests.c \
-	uvd_messages.h \
+	decode_messages.h \
 	vce_tests.c \
 	vce_ib.h \
 	frame.h \