configure: fix qemu-img name

Signed-off-by: NCleber Rosa <crosa@redhat.com>
Reviewed-by: NLaurent Vivier <laurent@vivier.eu>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190207193605.25676-3-crosa@redhat.com>
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>

configure

@@ -1768,7 +1768,7 @@ disabled with --disable-FEATURE, default is enabled if available:
   virglrenderer   virgl rendering support
   xfsctl          xfsctl support
   qom-cast-debug  cast debugging support
-  tools           build qemu-io, qemu-nbd and qemu-image tools
+  tools           build qemu-io, qemu-nbd and qemu-img tools
   vxhs            Veritas HyperScale vDisk backend support
   bochs           bochs image format support
   cloop           cloop image format support