drivers/video/pmag-ba-fb.c: improve diagnostics

Add error messages to the probe call.

While they may rarely trigger, they may be useful when something weird is
going on.  Also this is good style.

[akpm@linux-foundation.org: remove unneeded initialisation]
Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: Mariusz Kozlowski <m.kozlowski@tuxland.pl>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>