nor/at91sam3: change prototype of get_current_sam3()

nor/at91sam3: change prototype of get_current_sam3()

To prepare for handling TCL return values consistently, all calls
to command_print/command_print_sameline should be ready to switch
to CMD as first parameter.

Change prototype of get_current_sam3() to pass CMD instead of
CMD_CTX.

This change was part of http://openocd.zylin.com/1815 from Paul
Fertser and has been extracted and rebased to simplify the review.

Change-Id: Ia1e7af79d0fc89d229b4e10df37317a374bbab62
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5054
Tested-by: jenkins