x86, asm: Fix ancient-GAS workaround

It turns out to generate something like this:

    printk ( ("<3>") "something");

The extra parentheses here break the UML compile.

Change the sed-program to add the parentheses only for numbers.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
Acked-by: Jan Beulich <jbeulich@novell.com>
LKML-Reference: <1287696649.20421.1401306095@webmail.messagingengine.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>