include/linux/log2.h: mark is_power_of_2() with __always_inline

When building kernel with randconfig, there is an error:

In function `kvm_is_cr4_bit_set',inlined from
`kvm_update_cpuid_runtime' at arch/x86/kvm/cpuid.c:310:9:

include/linux/compiler_types.h:542:38: error: call to
`__compiletime_assert_380' declared with attribute error:
BUILD_BUG_ON failed: !is_power_of_2(cr4_bit).

'!is_power_of_2(X86_CR4_OSXSAVE)' is False, but gcc treats is_power_of_2()
as non-inline function and a compilation error happens. Fix this by marking
is_power_of_2() with __always_inline.

Link: https://lkml.kernel.org/r/20250221071624.1356899-1-suhui@nfschina.com
Signed-off-by: Su Hui <suhui@nfschina.com>
Cc: Binbin Wu <binbin.wu@linux.intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Su Hui

include/linux/log2.h

@@ -41,7 +41,7 @@ int __ilog2_u64(u64 n)
  * *not* considered a power of two.
  * Return: true if @n is a power of 2, otherwise false.
  */
-static inline __attribute__((const))
+static __always_inline __attribute__((const))
 bool is_power_of_2(unsigned long n)
 {
 	return (n != 0 && ((n & (n - 1)) == 0));