usb: dwc3-meson-g12a: fix usb2 PHY glue init when phy0 is disabled

commit 4d2aa178 upstream.

When only PHY1 is used (for example on Odroid-HC4), the regmap init code
uses the usb2 ports when doesn't initialize the PHY1 regmap entry.

This fixes:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
...
pc : regmap_update_bits_base+0x40/0xa0
lr : dwc3_meson_g12a_usb2_init_phy+0x4c/0xf8
...
Call trace:
regmap_update_bits_base+0x40/0xa0
dwc3_meson_g12a_usb2_init_phy+0x4c/0xf8
dwc3_meson_g12a_usb2_init+0x7c/0xc8
dwc3_meson_g12a_usb_init+0x28/0x48
dwc3_meson_g12a_probe+0x298/0x540
platform_probe+0x70/0xe0
really_probe+0xf0/0x4d8
driver_probe_device+0xfc/0x168
...

Fixes: 013af227

 ("usb: dwc3: meson-g12a: handle the phy and glue registers separately")
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210601084830.260196-1-narmstrong@baylibre.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>