build: avoid gcc 4.7 warning about inlines

build: avoid gcc 4.7 warning about inlines

gcc 4.7 complains:

util/virhashcode.c:49:17: error: always_inline function might not be inlinable [-Werror=attributes]
util/virhashcode.c:35:17: error: always_inline function might not be inlinable [-Werror=attributes]

Normal 'inline' is a hint that the compiler may ignore; the fact
that the function is static is good enough.  We don't care if the
compiler decided not to inline after all.

* src/util/virhashcode.c (getblock, fmix): Relax attribute.