phy-mvebu-a3700-utmi: correct typo in struct mvebu_a3700_utmi comments

We get warning with W=1 build:
drivers/phy/marvell/phy-mvebu-a3700-utmi.c:84: warning: Function
parameter or member 'usb_misc' not described in 'mvebu_a3700_utmi'

Fix that by correcting the typo usb_mis

Link: https://lore.kernel.org/r/20200708132809.265967-1-vkoul@kernel.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/phy/marvell/phy-mvebu-a3700-utmi.c

@@ -72,7 +72,7 @@ struct mvebu_a3700_utmi_caps {
  * struct mvebu_a3700_utmi - PHY driver data
  *
  * @regs: PHY registers
- * @usb_mis: Regmap with USB miscellaneous registers including PHY ones
+ * @usb_misc: Regmap with USB miscellaneous registers including PHY ones
  * @caps: PHY capabilities
  * @phy: PHY handle
  */