staging: mt7621-pci: delete release gpios related code

staging: mt7621-pci: delete release gpios related code

Making gpio8 and gpio9 vendor specific and putting them
into the specific dts file makes not needed to release
gpios anymore because we are not occupying those pins
in the first place if it is not necessary. When the
device tree is parsed we can also check and return for
the error because we rely in the fact that the related
device for the board is correct.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20200321072650.7784-3-sergio.paracuellos@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>