tools/xl: Call init function for libxl_domain_sched_params

tools/xl: Call init function for libxl_domain_sched_params

This patch calls init function for libxl_domain_sched_params before
passing it as reference to sched_domain_get() function in
tools/libxl/xl_cmdimpl.c
IDL generated libxl types should be used only after calling the init
function even if the variable is simply being passed by reference as
an output parameter to a libxl function

Signed-off-by: Uma Sharma <uma.sharma523@gmail.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
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