s390/boot: avoid unnecessary zeroing of .bss section

.bss section is a part of the decompressor's image now, linker fills it
with zeros already. No need do it with memset additionally.
Reviewed-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/boot/head.S

@@ -313,12 +313,6 @@ ENTRY(startup_kdump)
 	spt	6f-.LPG0(%r13)
 	mvc	__LC_LAST_UPDATE_TIMER(8),6f-.LPG0(%r13)
 	l	%r15,.Lstack-.LPG0(%r13)
-	// Clear decompressor's BSS section
-	larl	%r2,_bss
-	slgr	%r3,%r3
-	larl	%r4,_ebss
-	slgr	%r4,%r2
-	brasl	%r14,memset
 	brasl	%r14,verify_facilities
 	brasl	%r14,startup_kernel