dt-bindings: usb: max3421: Interrupt-parent is optional

Documentation modification, now interrupt-parent is an optional
property. Also fix few typos.
Signed-off-by: Jules Maselbas <jules.maselbas@grenoble-inp.org>
Reported-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/maxim,max3421.txt

 Maxim Integrated SPI-based USB 2.0 host controller MAX3421E
 
 Required properties:
- - compatible: "maxim,max3421"
+ - compatible: Should be "maxim,max3421"
  - spi-max-frequency: maximum frequency for this device must not exceed 26 MHz.
  - reg: chip select number to which this device is connected.
  - maxim,vbus-en-pin: <GPOUTx ACTIVE_LEVEL>
    GPOUTx is the number (1-8) of the GPOUT pin of MAX3421E to drive Vbus.
    ACTIVE_LEVEL is 0 or 1.
- - interrupt-parent: the phandle of the associated interrupt controller.
- - interrupts: the interuption line description for the interrupt controller.
+ - interrupts: the interrupt line description for the interrupt controller.
    The driver configures MAX3421E for active low level triggered interrupts,
    configure your interrupt line accordingly.
 
+Optional property:
+ - interrupt-parent: the phandle to the associated interrupt controller.
+
 Example:
 
 	usb@0 {