cpufreq: scmi: Account for malformed DT in scmi_dev_used_by_cpus()

Broadcom STB platforms were early adopters (2017) of the SCMI framework and as
a result, not all deployed systems have a Device Tree entry where SCMI
protocol 0x13 (PERFORMANCE) is declared as a clock provider, nor are the
CPU Device Tree node(s) referencing protocol 0x13 as their clock
provider. This was clarified in commit e11c480b ("dt-bindings:
firmware: arm,scmi: Extend bindings for protocol@13") in 2023.

For those platforms, we allow the checks done by scmi_dev_used_by_cpus()
to continue, and in the event of not having done an early return, we key
off the documented compatible string and give them a pass to continue to
use scmi-cpufreq.

Fixes: 6c9bb869 ("cpufreq: scmi: Skip SCMI devices that aren't used by the CPUs")
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>