doc: Fix copy-paste-error in virNodeGetMemoryStats

The description seems to be copied from virNodeGetCpuState.
Change wrong 'cpu' to 'memory'.
Signed-off-by: NPhilipp Hahn <hahn@univention.de>

src/libvirt.c

@@ -7661,7 +7661,7 @@ error:
  * @flags: extra flags; not used yet, so callers should always pass 0
  *
  * This function provides memory stats of the node.
- * If you want to get total cpu statistics of the node, you must specify
+ * If you want to get total memory statistics of the node, you must specify
  * VIR_NODE_MEMORY_STATS_ALL_CELLS to @cellNum.
  * The @params array will be filled with the values equal to the number of
  * stats suggested by @nparams