clk: stm32h7: Remove an unused field in struct stm32_fractional_divider

'mmask' has never been used in this driver.
Remove it.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/e08a470fbd6151ebd83a548714c08807a80a8ad0.1680364296.git.christophe.jaillet@wanadoo.frSigned-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/clk-stm32h7.c

@@ -667,7 +667,6 @@ struct stm32_fractional_divider {
 	void __iomem	*mreg;
 	u8		mshift;
 	u8		mwidth;
-	u32		mmask;
 
 	void __iomem	*nreg;
 	u8		nshift;