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 <[e-mail]>
Reported-by: Stephen Rothwell <[e-mail]>
Signed-off-by: Ming Lei <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/storage/protocol.c

···
 		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);