OMAP: DSS2: DSI: catch DSI errors in send_bta_sync

dsi_vc_send_bta_sync() waits for BTA interrupt with a 500ms timeout. If
a DSI error happens, no BTA is received and the timeout triggers. This
could be handled much faster by listening to DSI errors also.

This patch uses the ISR support to notice DSI errors while waiting for
the BTA, thus speeding up the fail-path considerably.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>