clk: microchip: use readl_poll_timeout() in pbclk_set_rate().

pbclk_set_rate() is using readl_poll_timeout_atomic() even
though spinlock is released. Fix it by replacing with
readl_poll_timeout().

Signed-off-by: Purna Chandra Mandal <purna.mandal@microchip.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>