The latest version of grep claims that egrep is now obsolete so the build
now contains warnings that look like:
        egrep: warning: egrep is obsolescent; using grep -E
fix this up by moving the vdso Makefile to use "grep -E" instead.

Cc: Julia Lawall <Julia.Lawall@inria.fr>
Cc: Nicolas Palix <nicolas.palix@imag.fr>
Cc: cocci@inria.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>