omap: Fix arch/arm/mach-omap2/mux.c: Off by one error

David Binderman ran the sourceforge tool cppcheck over the source code of the
new Linux kernel 2.6.33-rc6:

[./arm/mach-omap2/mux.c:492]: (error) Buffer access out-of-bounds

13 characters + 1 digit + 1 zero byte is more than 14 characters.

Also add a comment on mode0 name length in case new omaps
start using longer names.

Reported-by: David Binderman <dcb314@hotmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>