gas: xtensa: reuse find_trampoline_seg

gas: xtensa: reuse find_trampoline_seg

xtensa_create_trampoline_frag has opencoded fragment equivalent to
find_trampoline_seg. Drop the fragment and use find_trampoline_seg
instead. No functional changes.

gas/
2017-11-27  Max Filippov  <jcmvbkbc@gmail.com>

	* config/tc-xtensa.c (find_trampoline_seg): Move above the first
	use.
	(xtensa_create_trampoline_frag): Replace trampoline seg search
	code with a call to find_trampoline_seg.