powerpc: Remove initialisation of readpos

While powerpc doesn't use the seq_buf readpos, it did explicitly
initialise it for no good reason.

Link: https://lore.kernel.org/linux-trace-kernel/20231024145600.739451-1-willy@infradead.org

Cc: Christoph Hellwig <hch@lst.de>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Kees Cook <keescook@chromium.org>
Fixes: d0ed46b ("tracing: Move readpos from seq_buf to trace_seq")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: Matthew Wilcox (Oracle)

arch/powerpc/kernel/setup-common.c

@@ -601,7 +601,6 @@ struct seq_buf ppc_hw_desc __initdata = {
 	.buffer = ppc_hw_desc_buf,
 	.size = sizeof(ppc_hw_desc_buf),
 	.len = 0,
-	.readpos = 0,
 };
 
 static __init void probe_machine(void)