docs: i2c: smbus-protocol: fix typo

The subject is plural, fix the verb.
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

Documentation/i2c/smbus-protocol.rst

@@ -145,7 +145,7 @@ SMBus Write Word
 Implemented by i2c_smbus_write_word_data()
 
 This is the opposite of the Read Word operation. 16 bits
-of data is written to a device, to the designated register that is
+of data are written to a device, to the designated register that is
 specified through the Comm byte.::
 
   S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] P