hw/usb/core.c: reorder usage and assertion of p->ep

Reorder the code so the assertion of p->ep occurs before it is
used in the subsequent lines.

Signed-off-by: Sergei Heifetz <heifetz@yandex-team.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
1 file changed