qemu: conf: fix stray comma

qemu: conf: fix stray comma

The qemu.conf change broke our augeas test:

qemu/test_libvirtd_qemu.aug:96.3-203.1:exception thrown in test
qemu/test_libvirtd_qemu.aug:96.8-.34:exception: Iterated lens matched less than it should
    Lens: ../../src/qemu/libvirtd_qemu.aug:170.13-.43:
      Last match: ../../src/qemu/libvirtd_qemu.aug:18.52-.113:
      Not matching: ../../src/qemu/libvirtd_qemu.aug:12.19-.31:
    Error encountered at 48:27 (1615 characters into string)
    <\n    "/dev/ptmx", "/dev/kvm"|=|,\n]\nsave_image_format = "raw>

Fixes: ab5ba57012e9e6ab4f55afdeecd1813dd3ca916b
Signed-off-by: Ján Tomko <jtomko@redhat.com>