regmap: fix NULL deref on lookup

stable inclusion
from stable-v4.19.135
commit 7219c6b8fa24ec55a19d7a5ea58fb09151e37950
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8LTOI
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7219c6b8fa24ec55a19d7a5ea58fb09151e37950



-------------------------------------

commit c6df8433 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zhang Zekun <zhangzekun11@huawei.com>