video: valkyriefb: Fix unused variable warning in set_valkyrie_clock()

If CONFIG_ADB_CUDA=n:

drivers/video/fbdev/valkyriefb.c: In function ‘set_valkyrie_clock’:
drivers/video/fbdev/valkyriefb.c:267: warning: unused variable ‘i’
drivers/video/fbdev/valkyriefb.c:266: warning: unused variable ‘req’

Move the variable declarations inside the existing #ifdef section to fix
this.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>