Documentation/i2c: SMBus start signal is S not A

Just like all other I2C/SMBus commands, the start signal for the SMBus
Quick Command is S, not A.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Daniel Schaefer <git@danielschaefer.me>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

Documentation/i2c/smbus-protocol.rst

@@ -57,7 +57,7 @@ SMBus Quick Command
 
 This sends a single bit to the device, at the place of the Rd/Wr bit::
 
-  A Addr Rd/Wr [A] P
+  S Addr Rd/Wr [A] P
 
 Functionality flag: I2C_FUNC_SMBUS_QUICK