failure to compile, f_opendir arguments mismatch!

[xlla]

I'v encounter this issue while compile ooFatfs lib

ff.c:4438:11: error: too few arguments to function 'f_opendir'
     res = f_opendir(dp, path);      /* Open the target directory */

f_findfirst use 2 parameters to invoke f_opendir, but function f_opendir want an additional parameter FATFS *fs

[dpgeorge]

Thanks for the report. I've made a PR #9 to fix it.