gpio: etraxfs: fix set register flag
gpio: etraxfs: fix set register flag

BGPIO_F_UNREADABLE_REG_SET is incorrect, since the set register _is_
readable.  What's really required is BGPIO_F_READ_OUTPUT_REG_SET:
reading the set register reads the set output value.

Signed-off-by: Rabin Vincent <6bd3f43fd5b2b5689bccc97f6d09e3eb28307598@rab.in>
Signed-off-by: Linus Walleij <9cd9d802d23c0ed5e224beabf4ae4a5c478746ef@linaro.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs