Fixed typo in onewire generic doc

Onewire devices has 6 byte long unique serial numbers, 1 byte family
code and 1 byte CRC. Linux sysfs presents the device folder in the
form of familyID-deviceID, so CRC is not shown. The consequence is
that the device serial number is always a 12 long hex-string, but
doc says 13 in one place. This is corrected by this change.
Reference: https://en.wikipedia.org/wiki/1-WireSigned-off-by: NGergo Huszty <huszty.gergo@digitaltrip.hu>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/w1/w1.generic

@@ -76,7 +76,7 @@ See struct w1_bus_master definition in w1.h for details.
 
 w1 master sysfs interface
 ------------------------------------------------------------------
-<xx-xxxxxxxxxxxxx> - A directory for a found device. The format is family-serial
+<xx-xxxxxxxxxxxx>  - A directory for a found device. The format is family-serial
 bus                - (standard) symlink to the w1 bus
 driver             - (standard) symlink to the w1 driver
 w1_master_add      - (rw) manually register a slave device