[binutils-gdb] Update help text in disasm.c

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 7c9ee61b9f5fcad94fda11af1ab7469d78f17fbe ***

Author: Tom Tromey <tom@tromey.com>
Branch: master
Commit: 7c9ee61b9f5fcad94fda11af1ab7469d78f17fbe

Update help text in disasm.c

This changes some help text in disasm.c to follow the GNU style.

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

	* disasm.c (_initialize_disasm): Update help text.