Optimise swiotlb.c for size.

   text    data     bss     dec     hex filename
   5009      89      64    5162    142a lib/swiotlb.o-before
   4666      89      64    4819    12d3 lib/swiotlb.o-after

For some reason my gcc (4.0.2) doesn't want to tailcall these things.

swiotlb_sync_sg_for_device:
	pushq	%rbp	#
	movl	$1, %r8d	#,
	movq	%rsp, %rbp	#,
	call	swiotlb_sync_sg	#
	leave
	ret
	.size	swiotlb_sync_sg_for_device, .-swiotlb_sync_sg_for_device
	.section	.text.swiotlb_sync_sg_for_cpu,"ax",@progbits
.globl swiotlb_sync_sg_for_cpu
	.type	swiotlb_sync_sg_for_cpu, @function
swiotlb_sync_sg_for_cpu:
	pushq	%rbp	#
	xorl	%r8d, %r8d	#
	movq	%rsp, %rbp	#,
	call	swiotlb_sync_sg	#
	leave
	ret

Cc: Jan Beulich <jbeulich@novell.com>
Cc: Andi Kleen <ak@suse.de>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>