gpio: bd72720: handle missing regmap

gpio: bd72720: handle missing regmap

Currently the probe does not check whether getting the regmap succeeded.
This can cause crash when regmap is used, if it wasn't successfully
obtained. Failing to get the regmap is unlikely, especially since this
driver is expected to be kicked by the MFD driver only after registering
the regmap - but it is still better to handle this gracefully.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Fixes: e7eef0bd4075 ("regulator: bd71828-regulator.c: Fix LDON-HEAD mode")
Link: https://patch.msgid.link/5bfffee380863bcf24f3062e48094c8eb7b1342f.1775565381.git.mazziesaccount@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>