libsframe: stop search for SFrame FRE if its start IP is greater than PC

The SFrame FREs for an SFrame FDE are sorted on their start address.
Therefore the linear search for a matching SFrame FRE can be stopped,
if its start address is greater than the searched for PC.

libsframe/
	* sframe.c (sframe_find_fre): Stop search if FRE's start IP is
	greater than PC.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>