/dev/port: don't compile file operations without CONFIG_DEVPORT

(cherry picked from commit f0a816f)

In the future inb() and friends will not be available when compiling
with CONFIG_HAS_IOPORT=n so we must only try to access them here if
CONFIG_DEVPORT is set which depends on HAS_IOPORT.

Co-developed-by: Arnd Bergmann <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>
Signed-off-by: Niklas Schnelle <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
[mpe: Cherry picked from the char-misc tree to prevent build errors]
Signed-off-by: Michael Ellerman <[email protected]>

drivers/char/mem.c

@@ -383,6 +383,7 @@ static int mmap_mem(struct file *file, struct vm_area_struct *vma)
 	return 0;
 }
 
+#ifdef CONFIG_DEVPORT
 static ssize_t read_port(struct file *file, char __user *buf,
 			 size_t count, loff_t *ppos)
 {
@@ -424,6 +425,7 @@ static ssize_t write_port(struct file *file, const char __user *buf,
 	*ppos = i;
 	return tmp-buf;
 }
+#endif
 
 static ssize_t read_null(struct file *file, char __user *buf,
 			 size_t count, loff_t *ppos)
@@ -653,12 +655,14 @@ static const struct file_operations null_fops = {
 	.uring_cmd	= uring_cmd_null,
 };
 
-static const struct file_operations __maybe_unused port_fops = {
+#ifdef CONFIG_DEVPORT
+static const struct file_operations port_fops = {
 	.llseek		= memory_lseek,
 	.read		= read_port,
 	.write		= write_port,
 	.open		= open_port,
 };
+#endif
 
 static const struct file_operations zero_fops = {
 	.llseek		= zero_lseek,