soc: fsl: dpaa2-console: free buffer before returning from dpaa2_console_read

Free the kbuf buffer before returning from the dpaa2_console_read()
function. The variable no longer goes out of scope, leaking the storage
it points to.

Fixes: c93349d8

 ("soc: fsl: add DPAA2 console support")
Signed-off-by: Robert-Ionut Alexa <robert-ionut.alexa@nxp.com>
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Li Yang <leoyang.li@nxp.com>