V4L/DVB (10116): af9013: Fix gcc false warnings

drivers/media/dvb/frontends/af9013.c: In function ‘af9013_set_coeff’:
drivers/media/dvb/frontends/af9013.c:231: warning: ‘ns_coeff2_8k’ may be used uninitialized in this function
drivers/media/dvb/frontends/af9013.c:230: warning: ‘ns_coeff2_2k’ may be used uninitialized in this function
drivers/media/dvb/frontends/af9013.c:229: warning: ‘ns_coeff1_8193nu’ may be used uninitialized in this function
drivers/media/dvb/frontends/af9013.c:228: warning: ‘ns_coeff1_8192nu’ may be used uninitialized in this function
drivers/media/dvb/frontends/af9013.c:227: warning: ‘ns_coeff1_8191nu’ may be used uninitialized in this function
drivers/media/dvb/frontends/af9013.c:226: warning: ‘ns_coeff1_2048nu’ may be used uninitialized in this function
drivers/media/dvb/frontends/af9013.c: In function ‘af9013_update_snr’:
drivers/media/dvb/frontends/af9013.c:1012: warning: ‘snr_table’ may be used uninitialized in this function

Cc: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>