usb: gadget: udc: pxa27x_udc: Remove use of seq_printf return value

The seq_printf return value, because it's frequently misused,
will eventually be converted to void.

See: commit 1f33c41c03da ("seq_file: Rename seq_overflow() to
     seq_has_overflowed() and make public")

While there, simplify the error handler logic by returning
immediately and remove the unnecessary labels.

Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>