spi/spi-pl022: Call pl022_dma_remove(pl022) only if enable_dma is true

pl022_dma_remove() should be called only if enable_dma is true. There is no
point calling it when pl022_dma_probe() is not called, which again depends on
enable_dma.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>