powernow-k7: Fix CPU family number

Commit fa8031ae

 ('cpufreq: Add support
for x86 cpuinfo auto loading v4') seems to have inadvertently changed
the matched CPU family number from 6 to 7.  Change it back.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Acked-by: Thomas Renninger <trenn@suse.de>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>