regmap-irq: Fix bug in regmap_irq_get_irq_reg_linear()

irq_reg_stride in struct regmap_irq_chip is often 0, but that
actually means to use the default stride of 1. The effective
stride is stored in struct regmap_irq_chip_data->irq_reg_stride
and will get the corrected default value.

The default ->get_irq_reg() callback was using the stride from
the chip definition, which is wrong; fix it to use the effective
stride from the chip data instead.

Link: https://lore.kernel.org/lkml/acaaf77f-3282-8544-dd3c-7915fc1a6a4f@samsung.com/
Signed-off-by: Aidan MacDonald <aidanmacdonald.0x0@gmail.com>
Link: https://lore.kernel.org/r/20220704112847.23844-1-aidanmacdonald.0x0@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>