fix several issues in blas.jl

* L157: for `dot`: `BlasFloat` to `BlasReal`
  - BLAS `dot` only applies to real numbers
* L162: for `dotc`: `BlasFloat` to `BlasComplex`
  - BLAS `dotc` only applies to complex numbers
* L167: for `dotu`: `BlasFloat` to `BlasComplex`
  - BLAS `dotu` only applies to complex numbers
* L252: comment out line in `iamax`
  - or remove line
  - `x` is not an input variable
  - cannot compute length of a pointer
* L322: fix computation of length of output vector in `gbmv`
* L369: change `cgemv_` to `chemv_` in `hemv!`
Merge pull request #8407 from nwh/blas-bug-fix

fix several issues in blas.jl