memblock: Fix memblock_overlaps_memory()

This function always returns true, because it calls
memblock_overlaps_region() which returns a bool now. Change the
signature to bool and pass it on up instead.

Change-Id: I4b6403b823d20552a28006e35083d8056346dc51
Cc: Patrick Daly <pdaly@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>