parisc: Remove casts from atomic macros

The atomic operations on parisc are defined as macros. The macros
includes casts which disallows the use of some syntax elements and
produces error like this:

net/phonet/pep.c: In function 'pipe_rcv_status':
net/phonet/pep.c:262: error: lvalue required as left operand of assignment

The patch removes this superfluous casts.

Signed-off-by: Bastian Blank <waldi@debian.org>
Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>