Keep geom_uncompress(4) in line with geom_uzip(4), bring in the r264504 fix.

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