site: fix ac_cv_uint typo
Copy-pasting has resulted in a ac_cv_uint -> ac_cv_unit typo spreading
across the mips* site files, fix this.
(From OE-Core rev: 2b50faa9e7c3fea8480d608c4ef8c24837c7f52a)
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>