drm/cma: Fix recent regression of mmap() in the MMU case.

The stub get_unmapped_area() function was actually getting called, so
all of our mmap()s failed.

Cc: Yannick Fertre <yannick.fertre@st.com>
Fixes: 97bf3a9aa60f ("drm/cma: Update DEFINE_DRM_GEM_CMA_FOPS to add get_unmapped_area")
Signed-off-by: Eric Anholt <eric@anholt.net>
Link: http://patchwork.freedesktop.org/patch/msgid/20170417233124.18420-1-eric@anholt.net
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drm_gem_cma_helper.h

@@ -26,6 +26,13 @@ to_drm_gem_cma_obj(struct drm_gem_object *gem_obj)
 	return container_of(gem_obj, struct drm_gem_cma_object, base);
 }
 
+#ifndef CONFIG_MMU
+#define DRM_GEM_CMA_UNMAPPED_AREA_FOPS \
+	.get_unmapped_area	= drm_gem_cma_get_unmapped_area,
+#else
+#define DRM_GEM_CMA_UNMAPPED_AREA_FOPS
+#endif
+
 /**
  * DEFINE_DRM_GEM_CMA_FOPS() - macro to generate file operations for CMA drivers
  * @name: name for the generated structure
@@ -50,7 +57,7 @@ to_drm_gem_cma_obj(struct drm_gem_object *gem_obj)
 		.read		= drm_read,\
 		.llseek		= noop_llseek,\
 		.mmap		= drm_gem_cma_mmap,\
-		.get_unmapped_area	= drm_gem_cma_get_unmapped_area,\
+		DRM_GEM_CMA_UNMAPPED_AREA_FOPS \
 	}
 
 /* free GEM object */
@@ -86,15 +93,6 @@ unsigned long drm_gem_cma_get_unmapped_area(struct file *filp,
 					    unsigned long len,
 					    unsigned long pgoff,
 					    unsigned long flags);
-#else
-static inline unsigned long drm_gem_cma_get_unmapped_area(struct file *filp,
-							  unsigned long addr,
-							  unsigned long len,
-							  unsigned long pgoff,
-							  unsigned long flags)
-{
-	return -EINVAL;
-}
 #endif
 
 #ifdef CONFIG_DEBUG_FS