common: splash_source: fix cryptic error messages

common: splash_source: fix cryptic error messages

Some error messages emitted while loading the splash image are too
cryptic and don't provide any insights into the failure being a splash
related issue, such as 'Error (-2): cannot determine file size' etc.

This patch fixes the error codes by adding the function name to the
error print.

Signed-off-by: Anshul Dalal <anshuld@ti.com>
[trini: Add missing ',' and wrap to 80-width]
Signed-off-by: Tom Rini <trini@konsulko.com>