hwmon: ntc_thermistor: Fix typo (pullup-uV -> pullup-uv)

This patch fix typo of property name from 'pullup-uV' to 'pullup-uv'.
The ntc_thermistor.c use 'pullup-uv' when parsing dt data.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Naveen Krishna Chatradhi <ch.naveen@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>