parisc: fix frame pointer in ftrace_regs_caller()

The current code in ftrace_regs_caller() doesn't assign
%r3 to contain the address of the current frame. This
is hidden if the kernel is compiled with FRAME_POINTER,
but without it just crashes because it tries to dereference
an arbitrary address. Fix this by always setting %r3 to the
current stack frame.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Signed-off-by: Helge Deller <deller@gmx.de>