usb: gadget: functionfs: replace FFS_SETUP_STATUS with an inline function

The FFS_SETUP_STATUS macro could be trivialy replaced with an static
inline function but more importantly its name was tad confusing.
The name suggested it was a simple accessor macro but it actually
did change the state of the ffs_data structure perfomring
a FFS_SETUP_CANCELLED -> FFS_NO_SETUP transition.  The name of the
function -- ffs_setup_state_clear_cancelled -- should better
describe what the function actually does.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>