ARM: dts: AM33XX: Corrects typo in interrupt field in SPI node

DT field of "interrupts" was mentioned wrongly as "interrupt" in SPI
node. This went unnoticed as spi-omap2 driver not making use of
interrupt. Fixes the typo.

Signed-off-by: Philip Avinash <avinashphilip@ti.com>
Acked-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>