lib/crypto: sha256: Mark sha256_choose_blocks as __always_inline

lib/crypto: sha256: Mark sha256_choose_blocks as __always_inline

When the compiler chooses to not inline sha256_choose_blocks() in
the purgatory code, it fails to link against the missing CPU
specific version:

x86_64-linux-ld: arch/x86/purgatory/purgatory.ro: in function `sha256_choose_blocks.part.0':
sha256.c:(.text+0x6a6): undefined reference to `irq_fpu_usable'
sha256.c:(.text+0x6c7): undefined reference to `sha256_blocks_arch'
sha256.c:(.text+0x6cc): undefined reference to `sha256_blocks_simd'

Mark this function as __always_inline to prevent this, same as sha256_finup().

Fixes: 5b90a779bc54 ("crypto: lib/sha256 - Add helpers for block-based shash")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20250620191952.1867578-1-arnd@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>