ver_linux: make --version, use regex to find version number

Rely on regex to find the version number, rather than a field number.
Reduce the number of 'awk' invocations from two to one.

Signed-off-by: Alexander Kapshuk <alexander.kapshuk@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>