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: e84861fe ("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>