scmi_perf_fastchannels: Remove 'goto' from perf_fch_describe_fast_channels

The use of goto is discouraged, thus in this patch they are removed
from perf_fch_describe_fast_channels in place of a function helper.

Signed-off-by: Nicola Mazzucato <nicola.mazzucato@arm.com>
Change-Id: I695a26e5cd8f34b7d8ad8b7e2a6b28de9110c24d