powerpc/kernel: Convert mmu_has_feature() to returning bool

The intention is that the result is only used as a boolean, so enforce
that by changing the return type to bool.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/mmu.h

@@ -135,9 +135,9 @@ enum {
 		0,
 };
 
-static inline int mmu_has_feature(unsigned long feature)
+static inline bool mmu_has_feature(unsigned long feature)
 {
-	return (MMU_FTRS_POSSIBLE & cur_cpu_spec->mmu_features & feature);
+	return !!(MMU_FTRS_POSSIBLE & cur_cpu_spec->mmu_features & feature);
 }
 
 static inline void mmu_clear_feature(unsigned long feature)