spi: omap3: Fix multiple definition of 'priv'

Global definition of priv seems no-sense to use it
for non-dm case and pass the pointer to functions
which are common to both dm and non-dm.

So, fix this by removing omap3_spi_slave from non-dm
and make visible to omap3_spi_priv for both dm and non-dm.

Cc: Christophe Ricard <christophe-h.ricard@st.com>
Reported-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Jagan Teki <jteki@openedev.com>