android: boot: fix wrong end of header in v3/v4 parsing

android: boot: fix wrong end of header in v3/v4 parsing

The android boot header is page aligned but the current code made the
assumption that the header was always smaller than the current header
format.

When the page_size is defined as 2048, as this is the case with the
cuttlefish target, the current code sets the end of the header in the
middle of it as the v3 and v4 headers are respectively 2112 and 2128
bytes long.

Fix that by aligning to page_size

Fixes: 1115027d2f75 ("android: boot: update android_image_get_data to support v3, v4")
Signed-off-by: Guillaume Ranquet <ranquet.guillaume@gmail.com>