ver_linux: Assign constant RE to variable name for clarity

The regular expression that matches the version number of a utility
being queried is used as a constant expression in the current
implementation. Assigning the RE in question to a variable gives it a
meaningful name that clearly expresses the intended use of the expression
without having to think about the details of implementation.

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