bunzip2: fix off-by-one check

stage3-armv7a_hardfp-20130209.tar.bz2, 149189948 bytes long,
md5sum b29ce23312e14eb15a143377d4a38473, was failing to unpack.

It so happened that this file has a run which exactly fills
the 90k buffer. The check was "size >= bufsize", apparently
it has to be ">".

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

fix for bug https://jira.cyanogenmod.org/browse/CYAN-1896
Change-Id: I4e43fa2b84f2c00e627f75082d2250b4b4dff08e