Patch ssa

[leonardt]

Fixes issues in the ssa backend related to loading/storing of registered values

[coveralls]

Pull Request Test Coverage Report for Build 222

• 274 of 299 (91.64%) changed or added relevant lines in 8 files are covered.
• 36 unchanged lines in 7 files lost coverage.
• Overall coverage increased (+0.9%) to 72.778%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
silica/cfg/liveness.py	26	27	96.3%
silica/cfg/ssa.py	11	14	78.57%
silica/cfg/control_flow_graph.py	138	143	96.5%
silica/verilog.py	64	80	80.0%

Files with Coverage Reduction	New Missed Lines	%
silica/cfg/control_flow_graph.py	1	75.6%
silica/transformations/promote_widths.py	2	65.38%
silica/compile.py	3	84.66%
silica/transformations/constant_fold.py	3	73.33%
silica/verilog.py	6	82.93%
silica/coroutine.py	9	70.27%
silica/transformations/inline_functions.py	12	64.1%

Totals
Change from base Build 185:	0.9%
Covered Lines:	1433
Relevant Lines:	1969

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💛 - Coveralls