ApexInfo doesn't pass MinSdkVersion as string, but as ApiLevel

ApexInfo is not part of the properties struct. It can handle structs
having private fields.

Bug: 1663140
Test: m
Change-Id: Ib07d4410f0ce187c9de347da34b84b814b2eb537
diff --git a/apex/apex.go b/apex/apex.go
index 0eacf6d..f5e6fa9 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -903,7 +903,7 @@
 	// be built for this apexBundle.
 	apexInfo := android.ApexInfo{
 		ApexVariationName: mctx.ModuleName(),
-		MinSdkVersionStr:  minSdkVersion.String(),
+		MinSdkVersion:     minSdkVersion,
 		RequiredSdks:      a.RequiredSdks(),
 		Updatable:         a.Updatable(),
 		InApexes:          []string{mctx.ModuleName()},