gud: MobiCoreDriver: use mmap_lock instead of mmap_sem

We backported c2bad05b7b ("BACKPORT:
mmap locking API: rename mmap_sem to mmap_lock"), which renames the
mm_struct mmap_sem field to mmap_lock

Change-Id: Iaea6ee34f78ab721c09aae70cd30792f2c2a6584

drivers/gud/MobiCoreDriver/mmu.c

@@ -536,11 +536,7 @@ struct tee_mmu *tee_mmu_create(struct mm_struct *mm,
 			long gup_ret;
 
 			/* Buffer was allocated in user space */
-#if KERNEL_VERSION(5, 7, 19) < LINUX_VERSION_CODE
 			down_read(&mm->mmap_lock);
-#else
-			down_read(&mm->mmap_sem);
-#endif
 			/*
 			 * Always try to map read/write from a Linux PoV, so
 			 * Linux creates (page faults) the underlying pages if
@@ -558,11 +554,7 @@ struct tee_mmu *tee_mmu_create(struct mm_struct *mm,
 							   (uintptr_t)reader,
 							   nr_pages, 0, pages);
 			}
-#if KERNEL_VERSION(5, 7, 19) < LINUX_VERSION_CODE
 			up_read(&mm->mmap_lock);
-#else
-			up_read(&mm->mmap_sem);
-#endif
 			if (gup_ret < 0) {
 				ret = gup_ret;
 				mc_dev_err(ret, "failed to get user pages @%p",