arm64: cpufeature: Correctly display signed override values

When a field gets overriden, the kernel indicates the result of
the override in dmesg. This works well with unsigned fields, but
results in a pretty ugly output when the field is signed.

Truncate the field to its width before displaying it.
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20240122181344.258974-4-maz@kernel.orgSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/kernel/cpufeature.c

@@ -949,7 +949,8 @@ static void init_cpu_ftr_reg(u32 sys_reg, u64 new)
 				pr_warn("%s[%d:%d]: %s to %llx\n",
 					reg->name,
 					ftrp->shift + ftrp->width - 1,
-					ftrp->shift, str, tmp);
+					ftrp->shift, str,
+					tmp & (BIT(ftrp->width) - 1));
 		} else if ((ftr_mask & reg->override->val) == ftr_mask) {
 			reg->override->val &= ~ftr_mask;
 			pr_warn("%s[%d:%d]: impossible override, ignored\n",