pps: adjust references to actual name of uapi header file

pps: adjust references to actual name of uapi header file

Commit 86b525bed275 ("drivers pps: add PPS generators support") adds a file
entry in MAINTAINERS and a reference in the ioctl-number documentation
referring to the file pps-gen.h, whereas the file added in this commit is
named pps_gen.h.

Adjust the two references to the actual name of the uapi header file.
While at it, put the entry in MAINTAINERS at the right place for
alphabetical ordering.

Fixes: 86b525bed275 ("drivers pps: add PPS generators support")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Link: https://lore.kernel.org/r/20250110105000.56228-1-lukas.bulwahn@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>