VIDEO: mb86r0xgdc.c: fix warning: unused variable 'i'

Fix build warning:

Configuring for jadecpu board...
mb86r0xgdc.c: In function 'dsp_init':
mb86r0xgdc.c:60: warning: unused variable 'i'

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Anatolij Gustschin <agust@denx.de>