fix format string warnings in block-qcow2.c (Christoph Hellwig)

fix format string warnings in block-qcow2.c (Christoph Hellwig)

Recent patches added two compiler warnings about the format string
usage in qcow_read_extensions.  One is printing a uint64_t using
%lu which is incorrect on many platforms as it can be a unsigned
long long, the second one is printing the result of sizeof as
%lu, but it is a size_t so it needs to be printed using %zu.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6944 c046a42c-6fe2-441c-8c8c-71466251a162