staging: comedi: s626.c - fix multiline dereference

staging: comedi: s626.c - fix the following checkpatch issues:
WARNING: Avoid multiple line dereference - prefer 'devpriv->rps_buf.logical_base'
#1380: FILE: drivers/s626.c:1380:
+				   (unsigned long)devpriv->
+						  rps_buf.logical_base);

WARNING: Avoid multiple line dereference - prefer 'cmd->scan_begin_arg'
#1898: FILE: drivers/s626.c:1898:
+			err |= comedi_check_trigger_arg_min(&cmd->
+							    scan_begin_arg,

Signed-off-by: Roman Lakeev <sunnyddayss@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>