spi: pic32: Fix checking return value of devm_ioremap_resource

devm_ioremap_resource() returns ERR_PTR on error.
Also remove the redundant dev_err message, the implementation of
devm_ioremap_resource() already print error messages on error paths.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@kernel.org>