Fix incorrect check of bool returning function.

I changed elf_map_image from returning an int to returning bool.
Unfortunately, I forgot to change this one check. The result is
the relative pc of any relocation packed shared libraries is
wrong.

Bug: 21271675

(cherry picked from commit 6732d375)

Change-Id: I6fd4dc7e3e7b4a2f951a620c6fb95c93a2bcdfb5