clk: at91: programmable: remove unneeded register read

This register read is a leftover of a previous read/modify/write. We now use
regmap_update_bits(), so we don't need it anymore.

Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>