staging: sm750fb: Remove set but not used variable 'actual_mx_clk'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/staging/sm750fb/ddk750_chip.c: In function set_chip_clock:
drivers/staging/sm750fb/ddk750_chip.c:59:15: warning: variable actual_mx_clk set but not used [-Wunused-but-set-variable]

It is not used since commit f0977109 ("staging:
sm750fb: lower case to fix camelcase checkpatch warning")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/1570520515-2186-4-git-send-email-zhengbin13@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/sm750fb/ddk750_chip.c

@@ -56,7 +56,6 @@ static unsigned int get_mxclk_freq(void)
 static void set_chip_clock(unsigned int frequency)
 {
 	struct pll_value pll;
-	unsigned int actual_mx_clk;
 
 	/* Cheok_0509: For SM750LE, the chip clock is fixed. Nothing to set. */
 	if (sm750_get_chip_type() == SM750LE)
@@ -76,7 +75,7 @@ static void set_chip_clock(unsigned int frequency)
 		 * Return value of sm750_calc_pll_value gives the actual
 		 * possible clock.
 		 */
-		actual_mx_clk = sm750_calc_pll_value(frequency, &pll);
+		sm750_calc_pll_value(frequency, &pll);
 
 		/* Master Clock Control: MXCLK_PLL */
 		poke32(MXCLK_PLL_CTRL, sm750_format_pll_reg(&pll));