staging: lustre: libcfs: Prevent harmless read underflow

Because this is a post-op instead of a pre-op, then it means we check
if knl_buffer[-1] is a space. It doesn't really hurt anything, but
it causes a static checker warning so let's fix it.

Fixes: d7e09d0397e8 ("staging: add Lustre file system client support")
Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/lustre/lnet/libcfs/tracefile.c

···
 		return -EFAULT;
 
 	nob = strnlen(knl_buffer, usr_buffer_nob);
-	while (nob-- >= 0)		      /* strip trailing whitespace */
+	while (--nob >= 0)		      /* strip trailing whitespace */
 		if (!isspace(knl_buffer[nob]))
 			break;