Avoid a building error

&pDwmModule->config may equal to pConfig that triggers
a building error using gcc 4.7:

In file included from bionic/libc/include/signal.h:33:0,
                 from bionic/libc/include/sys/select.h:34,
                 from bionic/libc/include/unistd.h:34,
                 from system/core/include/cutils/log.h:34,
                 from frameworks/av/media/libeffects/downmix/EffectDownmix.c:19:
In function 'memcpy',
    inlined from 'Downmix_Configure' at frameworks/av/media/libeffects/downmix/EffectDownmix.c:651:11,
    inlined from 'Downmix_Init' at frameworks/av/media/libeffects/downmix/EffectDownmix.c:605:9,
    inlined from 'DownmixLib_Create' at frameworks/av/media/libeffects/downmix/EffectDownmix.c:233:9:
bionic/libc/include/string.h:114:31: error: call to '__memcpy_overlap_error' declared with attribute error: memcpy called with overlapping regions

Change-Id: Ia6c4aab72e38d00d8d526f3b56fc03b6530b4e44