USB: storage: fix compile warning

This patch should fix the below compile warning:

drivers/usb/storage/protocol.c: In function 'usb_stor_access_xfer_buf':
drivers/usb/storage/protocol.c:155:22: warning: comparison of distinct
pointer types lacks a cast [enabled by default]
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/storage/protocol.c

@@ -152,7 +152,8 @@ unsigned int usb_stor_access_xfer_buf(unsigned char *buffer,
 		return cnt;
 
 	while (sg_miter_next(&miter) && cnt < buflen) {
-		unsigned int len = min(miter.length, buflen - cnt);
+		unsigned int len = min_t(unsigned int, miter.length,
+				buflen - cnt);
 
 		if (dir == FROM_XFER_BUF)
 			memcpy(buffer + cnt, miter.addr, len);