remove RPM_BUILD_ROOT from asm-offsets.h

No file in rpm binary package should have the RPM_BUILD_ROOT string in it.
To simplify building of external modules, our kernel-source package
contains some temp files from the Kbuild system.  asm/asm-offsets.h is one
of the files that contains the absolute path if make O=$O is used.

  * This file was generated by /var/tmp/kernel-source-2.6.14_rc4-build/usr/src/linux-2.6.14-rc4-2/Kbuild

Remove the $RPM_BUILD_ROOT string in the shipped tempfile.

Signed-off-by: Olaf Hering <olh@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>