regulator: stm32-pwr: fix of_iomap leak

In the Linux kernel, the following vulnerability has been resolved: regulator: stm32-pwr: fix of_iomap leak Smatch reports: drivers/regulator/stm32-pwr.c:166 stm32_pwr_regulator_probe() warn: 'base' from of_iomap() not released on lines: 151,166. In stm32_pwr_regulator_probe(), base is not released when devm_kzalloc() fails to allocate memory or devm_regulator_register() fails to register a new regulator device, which may cause a leak. To fix this issue, replace of_iomap() with devm_platform_ioremap_resource(). devm_platform_ioremap_resource() is a specialized function for platform devices. It allows 'base' to be automatically released whether the probe function succeeds or fails. Besides, use IS_ERR(base) instead of !base as the return value of devm_platform_ioremap_resource() can either be a pointer to the remapped memory or an ERR_PTR() encoded error code if the operation fails.