spi: spi-ep93xx: Fix the PTR_ERR() argument

PTR_ERR should access the value just tested by IS_ERR.

The semantic patch that makes this change is available
in scripts/coccinelle/tests/odd_ptr_err.cocci.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>