rtapi fix shmem comment

Author: SebKuzminsky

src/rtapi/rtapi.h

@@ -431,11 +431,10 @@ RTAPI_BEGIN_DECLS
     'module_id' is the ID of the module that is making the call (see
     rtapi_init).  The block will be at least 'size' bytes, and may
     be rounded up.  Allocating many small blocks may be very wasteful.
-    When a particular block is allocated for the first time, the first
-    4 bytes are zeroed.  Subsequent allocations of the same block
+    When a particular block is allocated for the first time, all
+    bytes are zeroed.  Subsequent allocations of the same block
     by other modules or processes will not touch the contents of the
-    block.  Applications can use those bytes to see if they need to
-    initialize the block, or if another module already did so.
+    block.
     On success, it returns a positive integer ID, which is used for
     all subsequent calls dealing with the block.  On failure it
     returns a negative error code.  Call only from within user or