cmd/mr_create.go: Fix -f option

[prarit]

The -f option was reported to be broken. This occurred due to a coding error and this simple change will fix it.

Fix the -f option (-F and no options have also been verified to work).

[prarit]

@zampierilucas quick fix. Obviously broken.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.06 :tada:

Comparison is base (2bbd110) 55.56% compared to head (3218c3a) 55.62%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #872 +/- ## ========================================== + Coverage 55.56% 55.62% +0.06% ========================================== Files 82 82 Lines 5977 5977 ========================================== + Hits 3321 3325 +4 + Misses 2367 2364 -3 + Partials 289 288 -1 ``` | [Impacted Files](https://app.codecov.io/gh/zaquestion/lab/pull/872?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zaq%3F+Wiedmann) | Coverage Δ | | |---|---|---| | [cmd/mr\_create.go](https://app.codecov.io/gh/zaquestion/lab/pull/872?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zaq%3F+Wiedmann#diff-Y21kL21yX2NyZWF0ZS5nbw==) | `72.03% <100.00%> (ø)` | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/zaquestion/lab/pull/872/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zaq%3F+Wiedmann)

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