[SPARC64]: Typo in dtlb_backend.S, _PAGE_SZ4M --> _PAGE_SZ4MB

Noticed by Eddie C. Dost
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc64/kernel/dtlb_backend.S

@@ -16,7 +16,7 @@
 #elif PAGE_SHIFT == 19
 #define SZ_BITS		_PAGE_SZ512K
 #elif PAGE_SHIFT == 22
-#define SZ_BITS		_PAGE_SZ4M
+#define SZ_BITS		_PAGE_SZ4MB
 #endif
 
 #define VALID_SZ_BITS	(_PAGE_VALID | SZ_BITS)