USB: gadget: f_mass_storage: Fix unused variable warning

[ Upstream commit 55c3e57 ]

Fix a "variable set but not used" warning in f_mass_storage.c.  rc is
used if	verbose debugging is enabled but not otherwise.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Fixes: d5e2b67 ("USB: g_mass_storage: template f_mass_storage.c file created")
Link: https://lore.kernel.org/r/cfed16c7-aa46-494b-ba84-b0e0dc99be3a@rowland.harvard.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/usb/gadget/function/f_mass_storage.c

@@ -926,7 +926,7 @@ static void invalidate_sub(struct fsg_lun *curlun)
 {
 	struct file	*filp = curlun->filp;
 	struct inode	*inode = file_inode(filp);
-	unsigned long	rc;
+	unsigned long __maybe_unused	rc;
 
 	rc = invalidate_mapping_pages(inode->i_mapping, 0, -1);
 	VLDBG(curlun, "invalidate_mapping_pages -> %ld\n", rc);