dt-bindings: hwmon: ltc2978: add support for ltc7841

Add LTC7841 to supported devices of LTC2978. It has similar set of
registers to LTC7880, differing only in number of channels and
some unimplemented PMBUS status and functionalities.

Signed-off-by: Mariel Tinaco <Mariel.Tinaco@analog.com>

Author: MarielTinaco

Documentation/devicetree/bindings/hwmon/ltc2978.txt

@@ -16,6 +16,7 @@ Required properties:
   * "lltc,ltc3886"
   * "lltc,ltc3887"
   * "lltc,ltc3889"
+  * "lltc,ltc7841"
   * "lltc,ltc7880"
   * "lltc,ltm2987"
   * "lltc,ltm4664"
@@ -42,6 +43,7 @@ Valid names of regulators depend on number of supplies supported per device:
   * ltc3880, ltc3882, ltc3884, ltc3886, ltc3887, ltc3889 : vout0 - vout1
   * ltc7880 : vout0 - vout1
   * ltc3883 : vout0
+  * ltc7841 : vout0
   * ltm4664 : vout0 - vout1
   * ltm4675, ltm4676, ltm4677, ltm4678 : vout0 - vout1
   * ltm4680, ltm4686 : vout0 - vout1