fpga: altera-hps2fpga: fix multiple init of l3_remap_lock

The global spinlock `l3_remap_lock` is reinitialized every time the
"probe" function `alt_fpga_bridge_probe()` is called.  It should only be
initialized once.  Use `DEFINE_SPINLOCK()` to initialize it statically.

Fixes: e5f8efa5 ("ARM: socfpga: fpga bridge driver support")
Cc: <stable@vger.kernel.org> # 4.10+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-By: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Alan Tull <atull@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>