rocm: component disabled reason missing

[dbarry9]

When the rocm component is configured in a PAPI build, the disabled reason is an empty string if no device is present.

Here is example output from the papi_component_avail utility:

Compiled-in components:
Name: perf_event Linux perf_event CPU counters
Name: perf_event_uncore Linux perf_event CPU uncore and northbridge
Name: rocm GPU events and metrics via AMD ROCm-PL API
-> Disabled:
Name: sysdetect System info detection component

This issue is present building with both ROCm versions 5.7 and 6.2.