fftlib: bump SRCREV to latest
fftlib: bump SRCREV to latest

* As the fftlib sources are shared amongst multiple recipes, abstract
  SRC_URI to simplfy overrides.

Signed-off-by: Jacob Stiffler <0ec61db87821c27ca8ee6f3e24c6f93fdbb785d4@ti.com>

rcn-ee/meta-processor-sdk,rcn-ee/meta-processor-sdk,rcn-ee/meta-processor-sdk