staging: mt7621-spi: Remove references to nonexistent mt7621_spi_ops

This struct does not exist, and when it is looked up in the
compatibility tree, it returns null.  Remove these nonfunctional lines.

Signed-off-by: George Hilliard <thirtythreeforty@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>