arm64: mm: fix comment typo of pud_offset_phys()

Fix a typo in the comment of macro pud_offset_phys().
Signed-off-by: Xujun Leng <lengxujun2007@126.com>
Link: https://lore.kernel.org/r/20210825150526.12582-1-lengxujun2007@126.comSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/pgtable.h

@@ -715,7 +715,7 @@ static inline pud_t *p4d_pgtable(p4d_t p4d)
 	return (pud_t *)__va(p4d_page_paddr(p4d));
 }
 
-/* Find an entry in the frst-level page table. */
+/* Find an entry in the first-level page table. */
 #define pud_offset_phys(dir, addr)	(p4d_page_paddr(READ_ONCE(*(dir))) + pud_index(addr) * sizeof(pud_t))
 
 #define pud_set_fixmap(addr)		((pud_t *)set_fixmap_offset(FIX_PUD, addr))