board/netta/codec.c: Fix GCC 4.6 build warnings

board/netta/codec.c: Fix GCC 4.6 build warnings

Fix:
codec.c: In function 's_write_BR':
codec.c:1389:15: warning: variable 'v' set but not used
[-Wunused-but-set-variable]
codec.c: In function 's_write_OR':
codec.c:1400:15: warning: variable 'v' set but not used
[-Wunused-but-set-variable]
codec.c: In function 's_write_NR':
codec.c:1411:15: warning: variable 'v' set but not used
[-Wunused-but-set-variable]

Signed-off-by: Wolfgang Denk <wd@denx.de>