[binutils-gdb] Update memattr.c help strings

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 99806209a4f89fc76d338982239ab8c214df4b4d ***

Author: Tom Tromey <tom@tromey.com>
Branch: master
Commit: 99806209a4f89fc76d338982239ab8c214df4b4d

Update memattr.c help strings

This changes memattr.c to use the GNU style for help strings.

2018-04-29  Tom Tromey  <tom@tromey.com>

	* memattr.c (_initialize_mem): Update help string.