csky: Fixup warning by EXPORT_SYMBOL(kmap)

This a wrong code, and no kmap symbol for export.
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Arnd Bergmann <arnd@arndb.de>

arch/csky/mm/highmem.c

@@ -19,8 +19,6 @@ void kmap_flush_tlb(unsigned long addr)
 }
 EXPORT_SYMBOL(kmap_flush_tlb);
 
-EXPORT_SYMBOL(kmap);
-
 void *kmap_atomic_high_prot(struct page *page, pgprot_t prot)
 {
 	unsigned long vaddr;