KVM: ARM/arm64: fix non-const declaration of function returning const

Sparse kicks up about a type mismatch for kvm_target_cpu:

arch/arm64/kvm/guest.c:271:25: error: symbol 'kvm_target_cpu' redeclared with different type (originally declared at ./arch/arm64/include/asm/kvm_host.h:45) - different modifiers

so fix this by adding the missing const attribute to the function
declaration.

Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

arch/arm/include/asm/kvm_host.h

@@ -42,7 +42,7 @@
 
 struct kvm_vcpu;
 u32 *kvm_vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num, u32 mode);
-int kvm_target_cpu(void);
+int __attribute_const__ kvm_target_cpu(void);
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
 void kvm_reset_coprocs(struct kvm_vcpu *vcpu);
 

arch/arm64/include/asm/kvm_host.h

@@ -42,7 +42,7 @@
 #define KVM_VCPU_MAX_FEATURES 3
 
 struct kvm_vcpu;
-int kvm_target_cpu(void);
+int __attribute_const__ kvm_target_cpu(void);
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
 int kvm_arch_dev_ioctl_check_extension(long ext);