can: pch_can: fix error passive level test

The test (((errc & PCH_REC) >> 8) > 127) would always be false because
the receive error counter ((errc & PCH_REC) >> 8) is at most 127, where
PCH_REC is defined as 0x7f00.  To test whether the receive error counter
has reached the error passive level, the RP bit (15) should be used.

Signed-off-by: Xi Wang <xi.wang@gmail.com>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>