Fix nb_iterations calculation in tree-vect-loop-manip.c

We previously stored the number of loop iterations rather
than the number of latch iterations.

gcc/
2016-11-15  Richard Sandiford  <richard.sandiford@arm.com>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

	* tree-vect-loop-manip.c (slpeel_make_loop_iterate_ntimes): Set
	nb_iterations to the number of latch iterations rather than the
	number of loop iterations.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r242493