qtest/fuzz-lsi53c895a-test: set guest RAM to 2G

qtest/fuzz-lsi53c895a-test: set guest RAM to 2G

test_lsi_do_msgout_cancel_req does not run on machines with small size
memory. Reduce guest memory from 4G to 2G to alleviate the problem.

Reported-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Mauro Matteo Cascella <mcascell@redhat.com>
Message-Id: <20220902133853.834065-1-mcascell@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Thomas Huth <thuth@redhat.com>