parisc: Zero-initialize newly alloced memblock

Commit 4fe9e1d ("parisc: Drop bootmem and switch to memblock")
switched to the memblock allocator, but missed to zero-initialize the
newly allocated memblocks. This lead to crashes on some machines like
the rp3410.

Fixes: 4fe9e1d ("parisc: Drop bootmem and switch to memblock")
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/mm/init.c

@@ -105,6 +105,8 @@ static void * __init get_memblock(unsigned long size)
 	else
 		panic("get_memblock() failed.\n");
 
+	memset(__va(phys), 0, size);
+
 	return __va(phys);
 }