s390/bitops: remove small optimization to fix clang build

clang does not know about the 'b1' construct used in bitops inline
assembly. Since the plan is to use compiler atomic builtins anyway
there is no point in requesting clang support for this. Especially if
one considers that the kernel seems to be the only user of this.

With removing this small optimization it is possible to compile the
kernel also with -march=zEC12 and higher using clang.

Build error:

In file included from ./include/linux/bitops.h:32:
./arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 'oi        $0,${1:b}'
                        "oi     %0,%b1\n"
                        ^

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>