regmap: fix NULL deref on lookup

Not all regmaps have a name so make sure to check for that to avoid
dereferencing a NULL pointer when dev_get_regmap() is used to lookup a
named regmap.

Fixes: e84861f ("regmap: dev_get_regmap_match(): fix string comparison")
Cc: stable@vger.kernel.org      # 5.8
Cc: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20231006082104.16707-1-johan+linaro@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/regmap.c

@@ -1478,7 +1478,7 @@ static int dev_get_regmap_match(struct device *dev, void *res, void *data)
 
 	/* If the user didn't specify a name match any */
 	if (data)
-		return !strcmp((*r)->name, data);
+		return (*r)->name && !strcmp((*r)->name, data);
 	else
 		return 1;
 }