s390/ap: get rid of register asm in ap_dqap()

This is the second part of the cleanup for the header file ap.h
to remove the register asm statements. This patch deals with
the inline ap_dqap() function where within the assembler code
an odd register of an register pair is to be addressed.

[hca@linux.ibm.com: this intentionally breaks compilation with any
 clang compilers prior to llvm-project commit 458eac257377 ("[SystemZ]
 Support the 'N' code for the odd register in inline-asm.").
 This is hopefully the last clang kernel compile breakage caused by
 incompatibilities between gcc and clang.]

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