ALSA: pci/oxygen/xonar_wm87x6: remove always true condition

Fix W=1 warnings:

sound/pci/oxygen/xonar_wm87x6.c: In function ‘wm8776_write’:
sound/pci/oxygen/xonar_wm87x6.c:119:11: warning: comparison of
unsigned expression >= 0 is always true [-Wtype-limits]
  119 |   if (reg >= WM8776_HPLVOL && reg <= WM8776_DACMASTER)
      |           ^~
sound/pci/oxygen/xonar_wm87x6.c: In function ‘wm8766_write’:
sound/pci/oxygen/xonar_wm87x6.c:147:12: warning: comparison of
unsigned expression >= 0 is always true [-Wtype-limits]
  147 |   if ((reg >= WM8766_LDA1 && reg <= WM8766_RDA1) ||
      |            ^~

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200702193604.169059-17-pierre-louis.bossart@linux.intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>