mtd: m25p80: remove 'disabled' device check

It seems like the following commit was never necessary

    commit 5f949137
    Author: Shaohui Xie <Shaohui.Xie@freescale.com>
    Date:   Fri Oct 14 15:49:00 2011 +0800

        mtd: m25p80: don't probe device which has status of 'disabled'

because it duplicates the code in of_platform_device_create_pdata()
which ensures that 'disabled' nodes are never instantiated.

Also, drop the __maybe_unused.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Reviewed-by: Sourav Poddar <sourav.poddar@ti.com>
Reviewed-by: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: <devicetree@vger.kernel.org>