ramoops: fix compile failure on parisc

Fixes this:

drivers/char/ramoops.c: In function 'ramoops_init':
drivers/char/ramoops.c:221: error: implicit declaration of function 'IS_ERR'
drivers/char/ramoops.c:222: error: implicit declaration of function 'PTR_ERR'

If it actually builds on other platforms, it's probably getting
linux/err.h via some other #include.

Signed-off-by: James Bottomley <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/char/ramoops.c

···
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/kernel.h>
+#include <linux/err.h>
 #include <linux/module.h>
 #include <linux/kmsg_dump.h>
 #include <linux/time.h>