Fix some missed "beneath" conversions

Fix some missed "beneath" conversions

The buildbot pointed out that arm-linux-nat.c was not properly using
"beneath" as a method.  A search showed a few more places with this
issue.

Tested by the buildbot, though of course this only checked
arm-linux-nat.c.  Nevertheless I'm checking this in under the obvious
rule.

gdb/ChangeLog
2018-06-10  Tom Tromey  <tom@tromey.com>

	* procfs.c (procfs_target::xfer_partial): Use "beneath" as a
	method.
	* nto-procfs.c (nto_procfs_target::xfer_partial): Use "beneath" as
	a method.
	* go32-nat.c (go32_nat_target::xfer_partial): Use "beneath" as a
	method.
	* arm-linux-nat.c (arm_linux_nat_target::read_description): Use
	"beneath" as a method.
	* arm-fbsd-nat.c (arm_fbsd_nat_target::read_description):
	Use "beneath" as a method.