logger: use __FUNCTION__ instead of __PRETTY_FUNCTION__

This avoids a few long-name overflows, at the cost of less instructive
names in the case of C++ (specifically overloaded functions and class
methods).  This in turn is offset against the fact that we're logging
the filename and line numbers in any case.

Change-Id: I54101a0bb5f8cb9ef63ec12c5e0d4c8edafff9ed
Signed-off-by: Jaco Kroon <jaco@uls.co.za>