arm64: Mark call_smc_arch_workaround_1 as __maybe_unused

When building allnoconfig:

arch/arm64/kernel/cpu_errata.c:174:13: warning: unused function
'call_smc_arch_workaround_1' [-Wunused-function]
static void call_smc_arch_workaround_1(void)
            ^
1 warning generated.

Follow arch/arm and mark this function as __maybe_unused.

Fixes: 4db61fef ("arm64: kvm: Modernize __smccc_workaround_1_smc_start annotations")
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/cpu_errata.c

@@ -171,7 +171,7 @@ static void install_bp_hardening_cb(bp_hardening_cb_t fn,
 
 #include <linux/arm-smccc.h>
 
-static void call_smc_arch_workaround_1(void)
+static void __maybe_unused call_smc_arch_workaround_1(void)
 {
 	arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_1, NULL);
 }