reset: rzg2l-usbphy-ctrl: Check pwrrdy is valid before using it

The pwrrdy regmap_filed is allocated in rzg2l_usbphy_ctrl_pwrrdy_init()
only if the driver data is set to RZG2L_USBPHY_CTRL_PWRRDY. Check that
pwrrdy is valid before using it to avoid "Unable to handle kernel NULL
pointer dereference at virtual address" errors.

Fixes: c5b7cd9 ("reset: rzg2l-usbphy-ctrl: Add suspend/resume support")
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

Author: claudiubeznea

drivers/reset/reset-rzg2l-usbphy-ctrl.c

@@ -136,6 +136,9 @@ static int rzg2l_usbphy_ctrl_set_pwrrdy(struct regmap_field *pwrrdy,
 {
 	u32 val = power_on ? 0 : 1;
 
+	if (!pwrrdy)
+		return 0;
+
 	/* The initialization path guarantees that the mask is 1 bit long. */
 	return regmap_field_update_bits(pwrrdy, 1, val);
 }