regulator: s2mps11: Set default ramp delay for S2MPS11 LDOs

Driver did not provide default value for ramp delay for LDOs which lead
to warning in dmesg, e.g. on Odroid XU4:

[    1.486076] vdd_ldo9: ramp_delay not set
[    1.506875] vddq_mmc2: ramp_delay not set
[    1.523766] vdd_ldo15: ramp_delay not set
[    1.544702] vdd_sd: ramp_delay not set

The datasheet for all the S2MPS1x family is inconsistent here and does
not specify unambiguously the value of ramp delay for LDO. It mentions
30 mV/us in one timing diagram but then omits it completely in LDO
regulator characteristics table (it is specified for bucks).

However the vendor kernels for Galaxy S5 and Odroid XU3 use values of 12
mV/us or 24 mV/us.

Without the ramp delay value the consumers do not wait for voltage
settle after changing it. Although the proper value of ramp delay for
LDOs is unknown, it seems safer to use at least some value from
reference kernel than to leave it unset.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>