arm64: cpufeature: Add missing .field_width for GIC system registers

This was missed when making specification of a field standard.

Fixes: 0a2eec83 ("arm64: cpufeature: Always specify and use a field width for capabilities")
Reported-by: Qian Cai <quic_qiancai@quicinc.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220302134225.159217-1-broonie@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/cpufeature.c

@@ -1947,6 +1947,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.matches = has_useable_gicv3_cpuif,
 		.sys_reg = SYS_ID_AA64PFR0_EL1,
 		.field_pos = ID_AA64PFR0_GIC_SHIFT,
+		.field_width = 4,
 		.sign = FTR_UNSIGNED,
 		.min_field_value = 1,
 	},