[binutils-gdb] Remove cleanup in get_return_value

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 0749542484129e77a30f1089d6d671197be5035f ***

Author: Yao Qi <yao.qi@linaro.org>
Branch: master
Commit: 0749542484129e77a30f1089d6d671197be5035f

Remove cleanup in get_return_value

With regcache ctor, we can use it to create local object in
get_return_value (), so that the cleanup can be removed.

gdb:

2017-04-28  Yao Qi  <yao.qi@linaro.org>

	* infcmd.c (get_return_value): Use regcache ctor, and remove
	cleanup.