clk: bcm: rpi: Remove global pllb_arm clock pointer

clk: bcm: rpi: Remove global pllb_arm clock pointer

The pllb_arm clk_hw pointer in the raspberry_clk structure isn't used
anywhere but in the raspberrypi_register_pllb_arm.

Let's remove it, this will make our lives easier in future patches.

Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: linux-clk@vger.kernel.org
Acked-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/842859cf1a77478620f45049178a588448202858.1592210452.git-series.maxime@cerno.tech
Signed-off-by: Stephen Boyd <sboyd@kernel.org>