x86, asm: Fix binutils 2.15 build failure

Add parentheses around one pushl_cfi argument.

Commit df5d1874 "x86: Use {push,pop}{l,q}_cfi in more places"
caused GNU assembler 2.15 (Debian Sarge) to fail. It is still
failing as of commit 07bd8516 "x86, asm: Restore parentheses
around one pushl_cfi argument". This patch solves build failure
with GNU assembler 2.15.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Jan Beulich <jbeulich@novell.com>
Cc: heukelum@fastmail.fm
Cc: hpa@linux.intel.com
LKML-Reference: <201011160445.oAG4jGif079860@www262.sakura.ne.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>