xfs_fsr: guard against path string overflows

xfs_fsr: guard against path string overflows

gettmpname() and getparent() blindly copy strings
into a target array; be sure we limit the copy to
the size of the target and null terminate it.

I don't see a way to get here with a too-long name,
since most paths try to open or stat the file already,
but it can't hurt to be defensive.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Mark Tinguely <tinguely@sgi.com>