usb: gadget: f_uac2: fix calculation of uac2->p_interval

The p_interval should be less if the 'bInterval' at the descriptor
is larger, eg, if 'bInterval' is 5 for HS, the p_interval should be
8000 / 16 = 500.

It fixes the patch 9bb87f168931 ("usb: gadget: f_uac2: send
reasonably sized packets")

Cc: <stable@vger.kernel.org> # v3.18+
Fixes: 9bb87f168931 ("usb: gadget: f_uac2: send reasonably sized packets")
Acked-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/function/f_uac2.c

@@ -1162,14 +1162,14 @@ afunc_set_alt(struct usb_function *fn, unsigned intf, unsigned alt)
 			factor = 1000;
 		} else {
 			ep_desc = &hs_epin_desc;
-			factor = 125;
+			factor = 8000;
 		}
 
 		/* pre-compute some values for iso_complete() */
 		uac2->p_framesize = opts->p_ssize *
 				    num_channels(opts->p_chmask);
 		rate = opts->p_srate * uac2->p_framesize;
-		uac2->p_interval = (1 << (ep_desc->bInterval - 1)) * factor;
+		uac2->p_interval = factor / (1 << (ep_desc->bInterval - 1));
 		uac2->p_pktsize = min_t(unsigned int, rate / uac2->p_interval,
 					prm->max_psize);