rpm centos: add missing mysql-devel BuildRequires
rpm centos: add missing mysql-devel BuildRequires

[groonga-dev,01009]

Reported by wing. Thanks!!!

naoa/mroonga,mroonga/mroonga,naoa/mroonga,naoa/mroonga,naoa/mroonga,naoa/mroonga,yoku0825/mroonga,mroonga/mroonga,yoku0825/mroonga,yoku0825/mroonga,yoku0825/mroonga,mroonga/mroonga,yoku0825/mroonga,mroonga/mroonga,naoa/mroonga,yoku0825/mroonga