[compile] fix non-c99 regression in for() loop

[smokhov]

A recent commit 774570f introduced a compilation regression when compiling libfreenect and fakenect specifically on EL6 platforms, where it previously did not exist due to the introduced for(int i ..) declaration, which is also inconsistent with the rest of the code:

...
[ 83%] Building C object fakenect/CMakeFiles/fakenect.dir/fakenect.c.o
.../OpenISS/libfreenect/fakenect/fakenect.c: In function ‘freenect_init’:
.../OpenISS/libfreenect/fakenect/fakenect.c:532: error: ‘for’ loop initial declarations are only allowed in C99 mode
.../OpenISS/libfreenect/fakenect/fakenect.c:532: note: use option -std=c99 or -std=gnu99 to compile your code
make[2]: *** [fakenect/CMakeFiles/fakenect.dir/fakenect.c.o] Error 1
make[1]: *** [fakenect/CMakeFiles/fakenect.dir/all] Error 2
make: *** [all] Error 2

So this simple one-liner makes it all happy again.

[piedar]

Does your compiler support c99? I was considering converting the entire src/ directory to c99, but I have no stats on what compilers people use.

[piedar]

Looks good for now. Let's use #539 for any discussion about the future.