Make sure not to start I/O bigger than MAXPHYS bytes.
Quoting r264504:
When we detect the condition, we'll reduce the block count and perform
a "short" read. In g_uncompress_done() we need to consider the original
I/O length and stop early if we're about to deflate a block that we didn't
read. By using bio_completed in the cloned BIO and not bio_length to
check for this, we automatically and gracefully handle short reads that
our providers may be doing on top of the short reads we may initiate
ourselves.
Reviewed by: marcel
6f05733a1f