EmbeddedPkg: fix gcc build errors in AndroidBootImgLib

EmbeddedPkg: fix gcc build errors in AndroidBootImgLib

Commit dbd546a32d5a
("BaseTools: Add gcc flag to warn on void* pointer arithmetic")
does its work and triggers build errors in this library.
Update the affected code to build correctly again.

Cc: Pierre Gondois <pierre.gondois@arm.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Bob Feng<bob.c.feng@intel.com>
Reported-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Leif Lindholm <leif@nuviainc.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>