ARM: vfp ptrace: no point flushing hw context for PTRACE_GETVFPREGS

If we're only reading the VFP context via the ptrace call, there's
no need to invalidate the hardware context - we only need to do that
on PTRACE_SETVFPREGS.  This allows more efficient monitoring of a
traced task.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>