Fix harmless if statements with empty body, spotted by clang

Fix harmless if statements with empty body, spotted by clang

These clang errors are harmless but worth fixing:
  CC    ppc-softmmu/usb-ohci.o
/src/qemu/hw/usb-ohci.c:1104:59: error: if statement has empty body [-Wempty-body]
                          ohci->ctrl_head, ohci->ctrl_cur);
/src/qemu/hw/usb-ohci.c:1371:57: error: if statement has empty body [-Wempty-body]
        DPRINTF("usb-ohci: port %d: SUSPEND\n", portnum);
  CC    sparc64-softmmu/translate.o
/src/qemu/target-sparc/translate.c:3173:37: error: if statement has empty body [-Wempty-body]
                                    ; // XXX

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>