[media] drxk: Return -EINVAL if an invalid bandwidth is used

drivers/media/dvb/frontends/drxk_hard.c: In function ‘SetDVBT’:
drivers/media/dvb/frontends/drxk_hard.c:3766: warning: enumeration value ‘BANDWIDTH_5_MHZ’ not handled in switch
drivers/media/dvb/frontends/drxk_hard.c:3766: warning: enumeration value ‘BANDWIDTH_10_MHZ’ not handled in switch
drivers/media/dvb/frontends/drxk_hard.c:3766: warning: enumeration value ‘BANDWIDTH_1_712_MHZ’ not handled in switch

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>