regulator: lp87565: Add margin while populating ramp_delay

The slew rate might need a +/- 15% margin as per the latest data manual:

	http://www.ti.com/lit/ds/snvsb22/snvsb22.pdf



Hence take a conservative approach to program 85% of the original
hardware slew rate so that the software accommodates the margin
delay while voltage switching. Hence reduce the default ramp_delay
populated in the descriptors also by 15%.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>