powerpc/rtas-proc: remove unused RMO_READ_BUF_MAX

This constant is unused.
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210408140630.205502-3-nathanl@linux.ibm.com

arch/powerpc/kernel/rtas-proc.c

@@ -755,8 +755,6 @@ static int ppc_rtas_tone_volume_show(struct seq_file *m, void *v)
 	return 0;
 }
 
-#define RMO_READ_BUF_MAX 30
-
 /**
  * ppc_rtas_rmo_buf_show() - Describe RTAS-addressable region for user space.
  *