kdump: print a message in case parse_crashkernel_mem resulted in zero bytes

parse_crashkernel_mem() silently returns if we get zero bytes in the
parsing function. It is useful for debugging to add a message,
especially if the kernel cannot boot correctly.

Add a pr_info instead of pr_warn because it is expected behavior for
size = 0, eg. crashkernel=2G-4G:128M, size will be 0 in case system
memory is less than 2G.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Dave Young <[e-mail]>
Cc: Baoquan He <[e-mail]>
Cc: Vivek Goyal <[e-mail]>
Cc: Bhupesh Sharma <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

kernel/crash_core.c

···
 				return -EINVAL;
 			}
 		}
-	}
+	} else
+		pr_info("crashkernel size resulted in zero bytes\n");
 
 	return 0;
 }