usb: gadget: zero: Fix warning generated by kbuild

The kbuild test bot generated the warning:
	drivers/usb/gadget/function/f_sourcesink.c:1498: warning: comparison is
	always false due to limited range of data type

This patch fixes it.
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: NAmit Virdi <amit.virdi@st.com>
CC: Felipe Balbi <balbi@ti.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>

drivers/usb/gadget/function/f_sourcesink.c

@@ -1483,7 +1483,7 @@ static ssize_t f_ss_opts_int_interval_store(struct f_ss_opts *opts,
 				       const char *page, size_t len)
 {
 	int ret;
-	u8 num;
+	u32 num;
 
 	mutex_lock(&opts->lock);
 	if (opts->refcnt) {
@@ -1491,7 +1491,7 @@ static ssize_t f_ss_opts_int_interval_store(struct f_ss_opts *opts,
 		goto end;
 	}
 
-	ret = kstrtou8(page, 0, &num);
+	ret = kstrtou32(page, 0, &num);
 	if (ret)
 		goto end;