lib: Pass the correct align offset to bitmap_find_next_zero_area_off

bitmap_find_next_zero_area_off requires everything to be given in terms
of bits. genpool no longer keeps track of everything in terms of bits
so the start address must be shifted before passing to
bitmap_find_next_zero_area_off. Without this, if the start address
is unaligned, the code will not take this into account.

Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
(cherry picked from commit e8e5365f)

Change-Id: I5eca13f181d50e6f9f8f39c7440c6619a8edc69a
Signed-off-by: Sudhir Sharma <sudsha@codeaurora.org>