cpufreq/amd-pstate: convert mutex use to guard()

cpufreq/amd-pstate: convert mutex use to guard()

[ Upstream commit 6c093d5a5b73ec1caf1e706510ae6031af2f9d43 ]

Using scoped guard declaration will unlock mutexes automatically.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Link: https://lore.kernel.org/r/20241209185248.16301-5-mario.limonciello@amd.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Stable-dep-of: 3ace20038e19 ("cpufreq/amd-pstate: Fix cpufreq_policy ref counting")
Signed-off-by: Sasha Levin <sashal@kernel.org>