Documentation: i2c: dev: 'block process call' is supported

And it has been for a while (since 2012 at least), only it was not
documented. Add it.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

Documentation/i2c/dev-interface.rst

@@ -159,6 +159,8 @@ for details) through the following functions::
   __s32 i2c_smbus_read_word_data(int file, __u8 command);
   __s32 i2c_smbus_write_word_data(int file, __u8 command, __u16 value);
   __s32 i2c_smbus_process_call(int file, __u8 command, __u16 value);
+  __s32 i2c_smbus_block_process_call(int file, __u8 command, __u8 length,
+                                     __u8 *values);
   __s32 i2c_smbus_read_block_data(int file, __u8 command, __u8 *values);
   __s32 i2c_smbus_write_block_data(int file, __u8 command, __u8 length,
                                    __u8 *values);