V4L/DVB (7906): tuners/mxl5005s.c: don't define variables for enums

It doesn't seem to be intended that "tuner_modu_type" and
"MXL5005_ControlName" were global variables.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>