doc: Fix path for generated images in Kronos user guide

In the Kronos user guide, the path, for the generated images after
Arm System Ready IR Firmware Build is mentioned,
build/tmp_systemready-glibc/deploy/images/fvp-rd-kronos/ doesn't
exist. The path should be 
build/tmp_systemready/deploy/images/fvp-rd-kronos/

This commit fixes that.

Signed-off-by: Anna Bridge <anna.bridge@arm.com>