fs/resctrl: Pass error reading event through to user space

Reading of event data is managed through populating a struct rmid_read with
properties of event needing to be read. This data is dispatched to an
appropriate CPU and upon completion any error can be found in rmid_read::err,
or on success the event data will be in rmid_read::val.

rmid_read::err is not updated in the unlikely scenario that the reading of the
event was dispatched to a wrong CPU. If this ever occurs due to a bug in
resctrl the user space read will return "success" but the data reported will
be invalid.

Ensure accurate error reporting so that if there may be an issue with how
resctrl picks a CPU it could be learned with an error to user space instead of
silent failure.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Ben Horgan <ben.horgan@arm.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Link: https://patch.msgid.link/6b3c66a49788828bd8c04a6911bd74c91ccd56f3.1782857711.git.reinette.chatre@intel.com

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