usb: image: mdc800: Remove redundant assignment to variable retval

usb: image: mdc800: Remove redundant assignment to variable retval

The variable retval is being assigned a value that is not being read
and is being re-assigned a new value a couple of statements later.
The assignment is redundant and can be removed.

Cleans up clang scan warning:
drivers/usb/image/mdc800.c:634:2: warning: Value stored to 'retval'
is never read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20240207113730.2444296-1-colin.i.king@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>