Fix mkdir_p in skpbench

We were crashing when trying to write an image on android.

Bug: skia:
Change-Id: Id8a4e07ea2385838e122291530710e2e4e74dd8d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/205209
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
1 file changed