soc: microchip: sam-clk: optimize get_rate() for generic clocks

Obtain generic clock division ratio from the register instead of
from the variable to avoid wrong result caused by un-synced
division ratios.

Signed-off-by: Tony Han <tony.han@microchip.com>

Author: TonyHan11

soc/microchip/sam/common/clk-generated.c

@@ -135,6 +135,8 @@ static int clk_generated_get_rate(const struct device *dev,
 		LOG_ERR("get parent clock rate failed.");
 		return ret;
 	}
+
+	gck->gckdiv = FIELD_GET(PMC_PCR_GCLKDIV_Msk, status);
 	*rate /= (gck->gckdiv + 1);
 
 	return 0;