remoteproc: pru: Fix wrong success return value for fw events

remoteproc: pru: Fix wrong success return value for fw events

The irq_create_fwspec_mapping() returns a proper virq value on success
and 0 upon any failure. The pru_handle_intrmap() treats this as an error
and disposes all firmware event mappings correctly, but is returning
this incorrect value as is, letting the pru_rproc_start() interpret it
as a success and boot the PRU.

Fix this by returning an error value back upon any such failure. While
at this, revise the error trace to print some meaningful info about the
failed event.

Fixes: c75c9fdac66e ("remoteproc: pru: Add support for PRU specific interrupt configuration")
Signed-off-by: Suman Anna <s-anna@ti.com>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20210407155641.5501-3-s-anna@ti.com
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>