video: fbdev: atyfb: remove set but not used variable 'mach64RefFreq'

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

drivers/video/fbdev/aty/mach64_gx.c: In function ‘aty_var_to_pll_8398’:
drivers/video/fbdev/aty/mach64_gx.c:621:36: warning: variable
‘mach64RefFreq’ set but not used [-Wunused-but-set-variable]

It is never used, and so can be removed.

Signed-off-by: yu kuai <[e-mail]>
Cc: zhengbin <[e-mail]>
Cc: yi.zhang <[e-mail]>
[b.zolnierkie: minor patch summary fixup]
Signed-off-by: Bartlomiej Zolnierkiewicz <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/video/fbdev/aty/mach64_gx.c

···
 	u32 mhz100;		/* in 0.01 MHz */
 	u32 program_bits;
 	/* u32 post_divider; */
-	u32 mach64MinFreq, mach64MaxFreq, mach64RefFreq;
+	u32 mach64MinFreq, mach64MaxFreq;
 	u16 m, n, k = 0, save_m, save_n, twoToKth;
 
 	/* Calculate the programming word */
 	mhz100 = 100000000 / vclk_per;
 	mach64MinFreq = MIN_FREQ_2595;
 	mach64MaxFreq = MAX_FREQ_2595;
-	mach64RefFreq = REF_FREQ_2595;	/* 14.32 MHz */
 
 	save_m = 0;
 	save_n = 0;