parisc: Make EWOULDBLOCK be equal to EAGAIN on parisc

On Linux, only parisc uses a different value for EWOULDBLOCK which
causes a lot of troubles for applications not checking for both values.
Since the hpux compat is long dead, make EWOULDBLOCK behave the same as
all other architectures.

Signed-off-by: Guy Martin <gmsoft@tuxicoman.be>
Signed-off-by: Helge Deller <deller@gmx.de>