usb: gadget: f_fs: Fix ExtCompat documentation in uapi header

The code was fixed in
commit 53642399 ("usb: gadget: f_fs: Fix wrong check on reserved1 wof OS_DESC_EXT_COMPAT")
but the in-header documentation kept referencing 0 as the expected value.
Reference 1 instead as per original commit message.

Signed-off-by: Vincent Pelletier <plr.vincent@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>