ARM: dts: msm: correct PM8994 L18 pin control regulator name for msm8996

Change d7435240 ("ARM: dts: msm:
add PM8994 LDO 18 pin control regulator for msm8996") added a new
rpm-smd-regulator device for the pin control version of the
PM8994 LDO 18 regulator.  Unfortunately, it specified the same
device node name as used for the original LDO 18 regulator.  This
had the effect of removing the original LDO 18 regulator and
switching all of its consumers to the pin control version.

Correct this by changing the name of the LDO 18 pin control
device to regulator-l18-pin-ctrl.

Change-Id: I2311b7c54afa98365e497598f7fb4be787141860
CRs-Fixed: 978138
Signed-off-by: David Collins <collinsd@codeaurora.org>