fix typos "wich" -> "which"

Signed-off-by: Uwe Zeisberger <zeisberg@informatik.uni-freiburg.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

drivers/serial/mpc52xx_uart.c

@@ -40,7 +40,7 @@
  * and so on). So the PSC1 is mapped to /dev/ttyPSC0, PSC2 to /dev/ttyPSC1 and
  * so on. But be warned, it's an ABSOLUTE REQUIREMENT ! This is needed mainly
  * fpr the console code : without this 1:1 mapping, at early boot time, when we
- * are parsing the kernel args console=ttyPSC?, we wouldn't know wich PSC it
+ * are parsing the kernel args console=ttyPSC?, we wouldn't know which PSC it
  * will be mapped to.
  */