media: pt3: remove redundant assignment to mask

Variable mask is being set to 0x80 and then set to this value again
in the following for-loop. Remove the extraneous first setting of mask.
Cleans up clang warning:

drivers/media/pci/pt3/pt3_i2c.c:88:2: warning: Value stored to 'mask'
is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>