s390/cpcmd: fix inline assembly register clobbering

Register variables initialized using arithmetic. That leads to
kasan instrumentaton code corrupting the registers contents.
Follow GCC guidlines and use temporary variables for assigning
init values to register variables.

Fixes: 94c12cc7 ("[S390] Inline assembly cleanup.")
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/Local-Register-Variables.htmlSigned-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/kernel/cpcmd.c

@@ -37,10 +37,12 @@ static int diag8_noresponse(int cmdlen)
 
 static int diag8_response(int cmdlen, char *response, int *rlen)
 {
+	unsigned long _cmdlen = cmdlen | 0x40000000L;
+	unsigned long _rlen = *rlen;
 	register unsigned long reg2 asm ("2") = (addr_t) cpcmd_buf;
 	register unsigned long reg3 asm ("3") = (addr_t) response;
-	register unsigned long reg4 asm ("4") = cmdlen | 0x40000000L;
-	register unsigned long reg5 asm ("5") = *rlen;
+	register unsigned long reg4 asm ("4") = _cmdlen;
+	register unsigned long reg5 asm ("5") = _rlen;
 
 	asm volatile(
 		"	diag	%2,%0,0x8\n"