USB: gadget: legacy: remove redundant zero assignment to variable 'value'

The variable value is being assigned to zero but that value is never being
read.  Either value is being reassigned in the following if condition, or
it is never read and the function returns. In both cases the assignment is
redundant and can be removed. Cleans up clang warning:

drivers/usb/gadget/legacy/inode.c:1473:4: warning: Value stored to 'value'
is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>