Fix the following warning:

drivers/media/i2c/ds90ub913.c:488:9: warning: 'v' may be used uninitialized [-Wmaybe-uninitialized]
  488 |         ub913_write(priv, UB913_REG_GENERAL_CFG,
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  489 |                     v | UB913_REG_GENERAL_CFG_CRC_ERR_RESET);
      |                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/media/i2c/ds90ub913.c:477:12: note: 'v' was declared here
  477 |         u8 v, v1, v2;
      |            ^

Fix the warning by initializing the variable to 0. Proper error handling
here would be somewhat pointless, as we are just printing register
values, and the user will see an error about the failed i2c transaction.

Fixes: c158d0d4 ("media: i2c: add DS90UB913 driver")
Reported-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Closes: https://lore.kernel.org/all/a0180488-f7f5-8538-a8bb-52ae52912835@xs4all.nl/Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>