LoongArch: Fix build error due to backport

In 6.1 there is no pmdp_get() definition, so use *pmd directly, in order
to avoid such build error due to a recently backport:

arch/loongarch/mm/hugetlbpage.c: In function 'huge_pte_offset':
arch/loongarch/mm/hugetlbpage.c:50:25: error: implicit declaration of function 'pmdp_get'; did you mean 'ptep_get'?  [-Wimplicit-function-declaration]
   50 |         return pmd_none(pmdp_get(pmd)) ? NULL : (pte_t *) pmd;
      |                         ^~~~~~~~
      |                         ptep_get

Reported-by: Guenter Roeck <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Huacai Chen <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: chenhuacai

arch/loongarch/mm/hugetlbpage.c

@@ -47,7 +47,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr,
 				pmd = pmd_offset(pud, addr);
 		}
 	}
-	return pmd_none(pmdp_get(pmd)) ? NULL : (pte_t *) pmd;
+	return pmd_none(*pmd) ? NULL : (pte_t *) pmd;
 }
 
 /*