Correct misspelling of directory name

:Release Notes:
WEBOS_INSTALL_PERSISTENTSTORAGEDIR is now defined correctly.

:Detailed Notes:
WEBOS_INSTALL_PERSISTENTSTORAGEDIR had two characters transposed.

:Testing Performed:
Clean compile and then compiled a module which used it.

:QA Notes:

:Issues Addressed:
NONE - fixed in passing

Open-webOS-DCO-1.0-Signed-off-by: Keith Derrick <keith.derrick@lge.com>

Change-Id: Ic868211097fb5c2283c4d4842a2b053d04eca356
Reviewed-on: https://g2g.palm.com/3564
Reviewed-by: Build Verification
Reviewed-by: Keith Derrick <keith.derrick@lge.com>
Tested-by: Keith Derrick <keith.derrick@lge.com>