mailbox: qcom-apcs: fix max_register value

The mailbox length is 0x1000 hence the max_register value is 0xFFC.

Fixes: c6a8b171ca ("mailbox: qcom: Convert APCS IPC driver to use
regmap")
Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/qcom-apcs-ipc-mailbox.c

@@ -28,7 +28,7 @@ static const struct regmap_config apcs_regmap_config = {
 	.reg_bits = 32,
 	.reg_stride = 4,
 	.val_bits = 32,
-	.max_register = 0x1000,
+	.max_register = 0xFFC,
 	.fast_io = true,
 };