vesa: fix make distcheck.

Add missing compat-api header
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/Makefile.am

@@ -32,5 +32,6 @@ vesa_drv_la_LDFLAGS = -module -avoid-version
 vesa_drv_ladir = @moduledir@/drivers
 
 vesa_drv_la_SOURCES = \
+         compat-api.h \
          vesa.c \
          vesa.h