Make sys_pselect7 static

commit c9da9f2129d6a421c32e334a83770a9e67f7feac upstream.

Not a single architecture has wired up sys_pselect7 plus it is the
only system call with seven parameters. Just make it static and
rename it to do_pselect which will do the work for sys_pselect6.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>