cpufreq/amd-pstate: Catch failures for amd_pstate_epp_update_limit()

amd_pstate_set_epp() calls cppc_set_epp_perf() which can fail for
a variety of reasons but this is ignored.  Change the return flow
to allow failures.

Reviewed-by: Perry Yuan <perry.yuan@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>