usb: dwc2: gadget: Avoid pointless read of EP control register

Commit ec1f9d9f ("usb: dwc2: gadget: parity fix in isochronous mode") moved
these checks to dwc2_hsotg_change_ep_iso_parity() back in 2015.  The assigned
value hasn't been read back since.  Let's remove the unnecessary H/W read.

Fixes the following W=1 warning:

 drivers/usb/dwc2/gadget.c: In function ‘dwc2_hsotg_epint’:
 drivers/usb/dwc2/gadget.c:2981:6: warning: variable ‘ctrl’ set but not used [-Wunused-but-set-variable]
 2981 | u32 ctrl;
 | ^~~~

Cc: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Link: https://lore.kernel.org/r/20200715093209.3165641-3-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc2/gadget.c

@@ -2978,10 +2978,8 @@ static void dwc2_hsotg_epint(struct dwc2_hsotg *hsotg, unsigned int idx,
 	u32 epctl_reg = dir_in ? DIEPCTL(idx) : DOEPCTL(idx);
 	u32 epsiz_reg = dir_in ? DIEPTSIZ(idx) : DOEPTSIZ(idx);
 	u32 ints;
-	u32 ctrl;
 
 	ints = dwc2_gadget_read_ep_interrupts(hsotg, idx, dir_in);
-	ctrl = dwc2_readl(hsotg, epctl_reg);
 
 	/* Clear endpoint interrupts */
 	dwc2_writel(hsotg, ints, epint_reg);