vboxsf: remove redundant variable out_len

vboxsf: remove redundant variable out_len

The variable out_len is being used to accumulate the number of
bytes but it is not being used for any other purpose. The variable
is redundant and can be removed.

Cleans up clang scan build warning:
fs/vboxsf/utils.c:443:9: warning: variable 'out_len' set but not
used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20240229225138.351909-1-colin.i.king@gmail.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>