btrfs: remove unused parameter nr_pages in add_ra_bio_pages()

btrfs: remove unused parameter nr_pages in add_ra_bio_pages()

BugLink: https://bugs.launchpad.net/bugs/1969857
commit cd9255be6980012ad54f2d4fd3941bc2586e43e5 upstream.

Variable @nr_pages only gets increased but never used.  Remove it.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>