regulator: max77857: fix build error in max77857-regulator.c

regulator: max77857: fix build error in max77857-regulator.c

When using low verion gcc(7.5) to build the max77857-regulator driver,
got the following error:

drivers/regulator/max77857-regulator.c:312:16: error: initializer element is not constant
  .ramp_delay = max77857_ramp_table[0][0],

To fix this by introducing a macro RAMAP_DELAY_INIT_VAL to define the
value of max77857_ramp_table[0[0].

Fixes: af71cccadece ("regulator: max77857: Add ADI MAX77857/59/MAX77831 Regulator Support")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20230803113654.818640-1-yangyingliang@huawei.com
Signed-off-by: Mark Brown <broonie@kernel.org>