clk: actions: remove redundant assignment after a mask operation

The assignment operation after a & mask operation is redundant,
the &= operator can be replaced with just the & operator.

Cleans up a clang-scan warning:
drivers/clk/actions/owl-pll.c:28:9: warning: Although the value
stored to 'mul' is used in the enclosing expression, the value is
never actually read from 'mul' [deadcode.DeadStores]

Signed-off-by: Colin Ian King <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Stephen Boyd <[e-mail]>

drivers/clk/actions/owl-pll.c

···
 	else if (mul > pll_hw->max_mul)
 		mul = pll_hw->max_mul;
 
-	return mul &= mul_mask(pll_hw);
+	return mul & mul_mask(pll_hw);
 }
 
 static unsigned long _get_table_rate(const struct clk_pll_table *table,