[media] drxk_hard: fix a few warnings

drivers/media/dvb-frontends/drxk_hard.c:68:6: warning: no previous prototype for 'IsA1WithPatchCode' [-Wmissing-prototypes]
drivers/media/dvb-frontends/drxk_hard.c:73:6: warning: no previous prototype for 'IsA1WithRomCode' [-Wmissing-prototypes]
drivers/media/dvb-frontends/drxk_hard.c:192:12: warning: no previous prototype for 'Frac28a' [-Wmissing-prototypes]
drivers/media/dvb-frontends/drxk_hard.c:590:5: warning: no previous prototype for 'PowerUpDevice' [-Wmissing-prototypes]

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