ANDROID: block: fix some inline crypto bugs

While we're waiting for v7 of the inline crypto patchset, fix some bugs
that made it into the v6 patchset, including one that caused bios with
an encryption context to never be merged, and one that could cause
non-contiguous pages to incorrectly added to a bio.

Bug: 137270441
Change-Id: I3911fcd6c76b5c9063b86d6af6267ad990a46718
Signed-off-by: Eric Biggers <ebiggers@google.com>