[IA64] signal: remove redundant code in setup_sigcontext()

This patch removes some redundant code in the function setup_sigcontext().

The registers ar.ccv,b7,r14,ar.csd,ar.ssd,r2-r3 and r16-r31 are not
restored in restore_sigcontext() when (flags & IA64_SC_FLAG_IN_SYSCALL) is
true.  So we don't need to zero those variables in setup_sigcontext().

Signed-off-by: Shi Weihua <shiwh@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>