src/video/directfb/SDL_DirectFB_render.c: fix build

Build with directfb is broken due to a spurious '}' and a missing 'E'
since version 2.0.12 and https://hg.libsdl.org/SDL/rev/4c2dcf490cba:

/home/buildroot/autobuild/run/instance-2/output-1/build/sdl2-2.0.12/src/video/directfb/SDL_DirectFB_render.c: In function 'SetBlendMode':
/home/buildroot/autobuild/run/instance-2/output-1/build/sdl2-2.0.12/src/video/directfb/SDL_DirectFB_render.c:202:9: error: case label not within a switch statement
  202 |         case SDL_BLENDMODE_MUL:
      |         ^~~~

/home/buildroot/autobuild/run/instance-2/output-1/build/sdl2-2.0.12/src/video/directfb/SDL_DirectFB_render.c:205:67: error: 'DSBF_DSTCOLOR' undeclared (first use in this function); did you mean 'DSBF_DESTCOLOR'?
  205 |             SDL_DFB_CHECK(destsurf->SetSrcBlendFunction(destsurf, DSBF_DSTCOLOR));
      |                                                                   ^~~~~~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/83ccefee68c2800c0544e6f40fa8bc8ee6b67b77

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

src/video/directfb/SDL_DirectFB_render.c

@@ -198,11 +198,10 @@ SetBlendMode(DirectFB_RenderData * data, int blendMode,
             SDL_DFB_CHECK(destsurf->SetDstBlendFunction(destsurf, DSBF_SRCCOLOR));
 
             break;
-        }
         case SDL_BLENDMODE_MUL:
             data->blitFlags = DSBLIT_BLEND_ALPHACHANNEL;
             data->drawFlags = DSDRAW_BLEND;
-            SDL_DFB_CHECK(destsurf->SetSrcBlendFunction(destsurf, DSBF_DSTCOLOR));
+            SDL_DFB_CHECK(destsurf->SetSrcBlendFunction(destsurf, DSBF_DESTCOLOR));
             SDL_DFB_CHECK(destsurf->SetDstBlendFunction(destsurf, DSBF_INVSRCALPHA));
 
             break;