Documentation/ABI: Fix documentation inconsistency for mlxreg-io sysfs interfaces

Fix attribute name from "jtag_enable", which described twice to
"cpld3_version", which is expected to be instead of second appearance
of "jtag_enable".

Fixes: 2752e344 ("Documentation/ABI: Add new attribute for mlxreg-io sysfs interfaces")
Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>