acpi: Fix buffer overflow in do_acpi_dump()

When do_acpi_dump() converts the table name to upper case, pass the
actual size of the output buffer so that the null terminator doesn't get
written beyond the end of the buffer.

Signed-off-by: Andrew Scull <ascull@google.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Cc: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>