usb: phy: isp1301: Fix build warning when CONFIG_OF is disabled

Commit fd567653 ("usb: phy: isp1301: Add OF device ID table")
added an OF device ID table, but used the of_match_ptr() macro
that will lead to a build warning if CONFIG_OF symbol is disabled:

drivers/usb/phy//phy-isp1301.c:36:34: warning: ‘isp1301_of_match’ defined but not used [-Wunused-const-variable=]
 static const struct of_device_id isp1301_of_match[] = {
                                  ^~~~~~~~~~~~~~~~

Fixes: fd567653 ("usb: phy: isp1301: Add OF device ID table")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>