lis2ds12.{h,hpp}: add missing parameter description

Signed-off-by: Alex Tereschenko <alext.mkrs@gmail.com>

src/lis2ds12/lis2ds12.h

@@ -299,6 +299,7 @@ extern "C" {
      * Read contiguous registers into a buffer
      *
      * @param dev The device context
+     * @param reg The register to start the read from
      * @param buffer The buffer to store the results
      * @param len The number of registers to read
      * @return The number of bytes read, or -1 on error

src/lis2ds12/lis2ds12.hpp

@@ -292,6 +292,7 @@ namespace upm {
         /**
          * Read contiguous registers into a buffer
          *
+         * @param reg The register to start the read from
          * @param buffer The buffer to store the results
          * @param len The number of registers to read
          * @return The number of bytes read