cxl/mbox: Drop mbox_mutex comment

... we have lockdep for this.
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed by: Adam Manzanares <a.manzanares@samsung.com>
Link: https://lore.kernel.org/r/20220404021216.66841-2-dave@stgolabs.netSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/mbox.c

@@ -147,7 +147,7 @@ static const char *cxl_mem_opcode_to_name(u16 opcode)
  * @out: Caller allocated buffer for the output.
  * @out_size: Expected size of output.
  *
- * Context: Any context. Will acquire and release mbox_mutex.
+ * Context: Any context.
  * Return:
  *  * %>=0	- Number of bytes returned in @out.
  *  * %-E2BIG	- Payload is too large for hardware.