usb: storage: sddr09: Remove a set-but-not-used variable

The 'isnew' variable in 'sddr09_write_lba' function is set but never
used.

This has been detected by building the driver with W=1:

drivers/usb/storage/sddr09.c: In function ‘sddr09_write_lba’:
drivers/usb/storage/sddr09.c:873:17: warning: variable ‘isnew’ set but
not used [-Wunused-but-set-variable]
int i, result, isnew;
                 ^

Signed-off-by: Augusto Mecking Caringi <augustocaringi@gmail.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>